FAQ updates from Ian Barwick.
This commit is contained in:
parent
ad4ce7aa5b
commit
0896707ef6
175
doc/FAQ
175
doc/FAQ
@ -1,7 +1,7 @@
|
|||||||
|
|
||||||
Frequently Asked Questions (FAQ) for PostgreSQL
|
Frequently Asked Questions (FAQ) for PostgreSQL
|
||||||
|
|
||||||
Last updated: Fri Oct 11 13:54:56 EDT 2002
|
Last updated: Sun Oct 13 22:49:56 EDT 2002
|
||||||
|
|
||||||
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
|
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
|
||||||
|
|
||||||
@ -112,7 +112,7 @@
|
|||||||
|
|
||||||
General Questions
|
General Questions
|
||||||
|
|
||||||
1.1) What is PostgreSQL?
|
1.1) What is PostgreSQL? How is it pronounced?
|
||||||
|
|
||||||
PostgreSQL is pronounced Post-Gres-Q-L.
|
PostgreSQL is pronounced Post-Gres-Q-L.
|
||||||
|
|
||||||
@ -122,11 +122,11 @@
|
|||||||
replaces the PostQuel query language with an extended subset of SQL.
|
replaces the PostQuel query language with an extended subset of SQL.
|
||||||
PostgreSQL is free and the complete source is available.
|
PostgreSQL is free and the complete source is available.
|
||||||
|
|
||||||
PostgreSQL development is performed by a team of Internet developers
|
PostgreSQL development is performed by a team of developers who all
|
||||||
who all subscribe to the PostgreSQL development mailing list. The
|
subscribe to the PostgreSQL development mailing list. The current
|
||||||
current coordinator is Marc G. Fournier (scrappy@PostgreSQL.org). (See
|
coordinator is Marc G. Fournier (scrappy@PostgreSQL.org). (See section
|
||||||
below on how to join). This team is now responsible for all
|
1.6 on how to join). This team is now responsible for all development
|
||||||
development of PostgreSQL.
|
of PostgreSQL.
|
||||||
|
|
||||||
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
|
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
|
||||||
others have contributed to the porting, testing, debugging, and
|
others have contributed to the porting, testing, debugging, and
|
||||||
@ -183,18 +183,22 @@
|
|||||||
Client
|
Client
|
||||||
|
|
||||||
It is possible to compile the libpq C library, psql, and other
|
It is possible to compile the libpq C library, psql, and other
|
||||||
interfaces and binaries to run on MS Windows platforms. In this case,
|
interfaces and client applications to run on MS Windows platforms. In
|
||||||
the client is running on MS Windows, and communicates via TCP/IP to a
|
this case, the client is running on MS Windows, and communicates via
|
||||||
server running on one of our supported Unix platforms. A file
|
TCP/IP to a server running on one of our supported Unix platforms. A
|
||||||
win31.mak is included in the distribution for making a Win32 libpq
|
file win32.mak is included in the distribution for making a Win32
|
||||||
library and psql. PostgreSQL also communicates with ODBC clients.
|
libpq library and psql. PostgreSQL also communicates with ODBC
|
||||||
|
clients.
|
||||||
|
|
||||||
Server
|
Server
|
||||||
|
|
||||||
The database server can run on Windows NT and Win2k using Cygwin, the
|
The database server can run on Windows NT and Win2k using Cygwin, the
|
||||||
Cygnus Unix/NT porting library. See pgsql/doc/FAQ_MSWIN in the
|
Cygnus Unix/NT porting library. See pgsql/doc/FAQ_MSWIN in the
|
||||||
distribution or the MS Windows FAQ on our web site. We have no plan to
|
distribution or the MS Windows FAQ at
|
||||||
do a native port to any Microsoft platform.
|
http://www.PostgreSQL.org/docs/faq-mswin.html.
|
||||||
|
|
||||||
|
A native port to some Microsoft platforms is currently being worked
|
||||||
|
upon.
|
||||||
|
|
||||||
1.5) Where can I get PostgreSQL?
|
1.5) Where can I get PostgreSQL?
|
||||||
|
|
||||||
@ -240,7 +244,7 @@
|
|||||||
Unix command irc -c '#PostgreSQL' "$USER" irc.phoenix.net.
|
Unix command irc -c '#PostgreSQL' "$USER" irc.phoenix.net.
|
||||||
|
|
||||||
A list of commercial support companies is available at
|
A list of commercial support companies is available at
|
||||||
http://www.postgresql.org/users-lounge/commercial-support.html.
|
http://www.PostgreSQL.org/users-lounge/commercial-support.html.
|
||||||
|
|
||||||
1.7) What is the latest release?
|
1.7) What is the latest release?
|
||||||
|
|
||||||
@ -258,9 +262,9 @@
|
|||||||
There are two PostgreSQL books available online at
|
There are two PostgreSQL books available online at
|
||||||
http://www.PostgreSQL.org/docs/awbook.html and
|
http://www.PostgreSQL.org/docs/awbook.html and
|
||||||
http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL
|
http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL
|
||||||
books available for purchase at http://www.postgresql.org/books/.
|
books available for purchase at http://www.ca.PostgreSQL.org/books/.
|
||||||
There is also a collection of PostgreSQL technical articles at
|
There is also a collection of PostgreSQL technical articles at
|
||||||
http://techdocs.postgresql.org/.
|
http://techdocs.PostgreSQL.org/.
|
||||||
|
|
||||||
psql has some nice \d commands to show information about types,
|
psql has some nice \d commands to show information about types,
|
||||||
operators, functions, aggregates, etc.
|
operators, functions, aggregates, etc.
|
||||||
@ -307,8 +311,9 @@
|
|||||||
|
|
||||||
1.13) How do I submit a bug report?
|
1.13) How do I submit a bug report?
|
||||||
|
|
||||||
Please visit the PostgreSQL BugTool page, which gives guidelines and
|
Please visit the PostgreSQL BugTool page at
|
||||||
directions on how to submit a bug.
|
http://www.PostgreSQL.org/bugs/bugs.php, which gives guidelines and
|
||||||
|
directions on how to submit a bug report.
|
||||||
|
|
||||||
Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if
|
Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if
|
||||||
there is a more recent PostgreSQL version or patches.
|
there is a more recent PostgreSQL version or patches.
|
||||||
@ -346,14 +351,14 @@
|
|||||||
compare favorably to other database software in this area.
|
compare favorably to other database software in this area.
|
||||||
|
|
||||||
Support
|
Support
|
||||||
Our mailing list provides a large group of developers and users
|
Our mailing lists provide contact with a large group of
|
||||||
to help resolve any problems encountered. While we can not
|
developers and users to help resolve any problems encountered.
|
||||||
guarantee a fix, commercial DBMSs do not always supply a fix
|
While we cannot guarantee a fix, commercial DBMSs do not always
|
||||||
either. Direct access to developers, the user community,
|
supply a fix either. Direct access to developers, the user
|
||||||
manuals, and the source code often make PostgreSQL support
|
community, manuals, and the source code often make PostgreSQL
|
||||||
superior to other DBMSs. There is commercial per-incident
|
support superior to other DBMSs. There is commercial
|
||||||
support available for those who need it. (See support FAQ
|
per-incident support available for those who need it. (See FAQ
|
||||||
item.)
|
section 1.6.)
|
||||||
|
|
||||||
Price
|
Price
|
||||||
We are free for all use, both commercial and non-commercial.
|
We are free for all use, both commercial and non-commercial.
|
||||||
@ -362,9 +367,9 @@
|
|||||||
|
|
||||||
1.15) How can I financially assist PostgreSQL?
|
1.15) How can I financially assist PostgreSQL?
|
||||||
|
|
||||||
PostgreSQL has had a first-class infrastructure since we started six
|
PostgreSQL has had a first-class infrastructure since we started in
|
||||||
years ago. This is all thanks to Marc Fournier, who has created and
|
1994. This is all thanks to Marc Fournier, who has created and managed
|
||||||
managed this infrastructure over the years.
|
this infrastructure over the years.
|
||||||
|
|
||||||
Quality infrastructure is very important to an open-source project. It
|
Quality infrastructure is very important to an open-source project. It
|
||||||
prevents disruptions that can greatly delay forward movement of the
|
prevents disruptions that can greatly delay forward movement of the
|
||||||
@ -373,8 +378,7 @@
|
|||||||
Of course, this infrastructure is not cheap. There are a variety of
|
Of course, this infrastructure is not cheap. There are a variety of
|
||||||
monthly and one-time expenses that are required to keep it going. If
|
monthly and one-time expenses that are required to keep it going. If
|
||||||
you or your company has money it can donate to help fund this effort,
|
you or your company has money it can donate to help fund this effort,
|
||||||
please go to https://store.pgsql.com/shopping/index.php?id=1 and make
|
please go to http://store.pgsql.com/shopping/ and make a donation.
|
||||||
a donation.
|
|
||||||
|
|
||||||
Although the web page mentions PostgreSQL, Inc, the "contributions"
|
Although the web page mentions PostgreSQL, Inc, the "contributions"
|
||||||
item is solely to support the PostgreSQL project and does not fund any
|
item is solely to support the PostgreSQL project and does not fund any
|
||||||
@ -407,39 +411,37 @@
|
|||||||
A nice introduction to Database-backed Web pages can be seen at:
|
A nice introduction to Database-backed Web pages can be seen at:
|
||||||
http://www.webreview.com
|
http://www.webreview.com
|
||||||
|
|
||||||
There is also one at http://www.phone.net/home/mwm/hotlist/.
|
|
||||||
|
|
||||||
For Web integration, PHP is an excellent interface. It is at
|
For Web integration, PHP is an excellent interface. It is at
|
||||||
http://www.php.net.
|
http://www.php.net.
|
||||||
|
|
||||||
For complex cases, many use the Perl interface and CGI.pm.
|
For complex cases, many use the Perl interface and CGI.pm or mod_perl.
|
||||||
|
|
||||||
2.3) Does PostgreSQL have a graphical user interface? A report generator?
|
2.3) Does PostgreSQL have a graphical user interface? A report generator?
|
||||||
An embedded query language interface?
|
An embedded query language interface?
|
||||||
|
|
||||||
We have a nice graphical user interface called pgaccess, which is
|
We have a nice graphical user interface called PgAccess, which is
|
||||||
shipped as part of the distribution. pgaccess also has a report
|
shipped as part of the distribution. PgAccess also has a report
|
||||||
generator. The Web page is http://www.flex.ro/pgaccess
|
generator. The Web page is http://www.pgaccess.org/.
|
||||||
|
|
||||||
We also include ecpg, which is an embedded SQL query language
|
We also include ecpg, which is an embedded SQL query language
|
||||||
interface for C.
|
interface for C.
|
||||||
|
|
||||||
2.4) What languages are available to communicate with PostgreSQL?
|
2.4) What languages are able to communicate with PostgreSQL?
|
||||||
|
|
||||||
We have:
|
We have:
|
||||||
* C (libpq)
|
* C (libpq)
|
||||||
* C++ (libpq++)
|
* C++ (libpq++)
|
||||||
* Embedded C (ecpg)
|
* Embedded C (ecpg)
|
||||||
* Java (jdbc)
|
* Java (jdbc)
|
||||||
* Perl (perl5)
|
* Perl (DBD::Pg)
|
||||||
* ODBC (odbc)
|
* ODBC (odbc)
|
||||||
* Python (PyGreSQL)
|
* Python (PyGreSQL)
|
||||||
* TCL (libpgtcl)
|
* TCL (libpgtcl)
|
||||||
* C Easy API (libpgeasy)
|
* C Easy API (libpgeasy)
|
||||||
* Embedded HTML (PHP from http://www.php.net)
|
* PHP ('pg_' functions, Pear::DB)
|
||||||
|
|
||||||
Additional interfaces are available at
|
Additional interfaces are available at
|
||||||
http://www.postgresql.org/interfaces.html.
|
http://www.PostgreSQL.org/interfaces.html.
|
||||||
_________________________________________________________________
|
_________________________________________________________________
|
||||||
|
|
||||||
Administrative Questions
|
Administrative Questions
|
||||||
@ -594,7 +596,7 @@
|
|||||||
was 64, and changing it required a rebuild after altering the
|
was 64, and changing it required a rebuild after altering the
|
||||||
MaxBackendId constant in include/storage/sinvaladt.h.
|
MaxBackendId constant in include/storage/sinvaladt.h.
|
||||||
|
|
||||||
3.9) What are the pg_sorttempNNN.NN files in my database directory?
|
3.9) What are the pg_tempNNN.NN files in my database directory?
|
||||||
|
|
||||||
They are temporary files generated by the query executor. For example,
|
They are temporary files generated by the query executor. For example,
|
||||||
if a sort needs to be done to satisfy an ORDER BY, and the sort
|
if a sort needs to be done to satisfy an ORDER BY, and the sort
|
||||||
@ -610,11 +612,11 @@
|
|||||||
|
|
||||||
The PostgreSQL team makes only small changes between minor releases,
|
The PostgreSQL team makes only small changes between minor releases,
|
||||||
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
||||||
However, major releases often change the internal format of system
|
However, major releases (e.g. from 7.2 to 7.3) often change the
|
||||||
tables and data files. These changes are often complex, so we don't
|
internal format of system tables and data files. These changes are
|
||||||
maintain backward compatability for data files. A dump outputs data in
|
often complex, so we don't maintain backward compatability for data
|
||||||
a generic format that can then be loaded in using the new internal
|
files. A dump outputs data in a generic format that can then be loaded
|
||||||
format.
|
in using the new internal format.
|
||||||
|
|
||||||
In releases where the on-disk format does not change, the pg_upgrade
|
In releases where the on-disk format does not change, the pg_upgrade
|
||||||
script can be used to upgrade without a dump/restore. The release
|
script can be used to upgrade without a dump/restore. The release
|
||||||
@ -632,10 +634,10 @@
|
|||||||
See the FETCH manual page, or use SELECT ... LIMIT....
|
See the FETCH manual page, or use SELECT ... LIMIT....
|
||||||
|
|
||||||
The entire query may have to be evaluated, even if you only want the
|
The entire query may have to be evaluated, even if you only want the
|
||||||
first few rows. Consider a query that has an ORDER BY. If there is an
|
first few rows. Consider using a query that has an ORDER BY. If there
|
||||||
index that matches the ORDER BY, PostgreSQL may be able to evaluate
|
is an index that matches the ORDER BY, PostgreSQL may be able to
|
||||||
only the first few records requested, or the entire query may have to
|
evaluate only the first few records requested, or the entire query may
|
||||||
be evaluated until the desired rows have been generated.
|
have to be evaluated until the desired rows have been generated.
|
||||||
|
|
||||||
4.3) How do I get a list of tables or other things I can see in psql?
|
4.3) How do I get a list of tables or other things I can see in psql?
|
||||||
|
|
||||||
@ -647,7 +649,8 @@
|
|||||||
|
|
||||||
4.4) How do you remove a column from a table?
|
4.4) How do you remove a column from a table?
|
||||||
|
|
||||||
We do not support ALTER TABLE DROP COLUMN, but do this:
|
Prior to version 7.3, ALTER TABLE DROP COLUMN is not supported. You
|
||||||
|
can do this instead:
|
||||||
BEGIN;
|
BEGIN;
|
||||||
LOCK TABLE old_table;
|
LOCK TABLE old_table;
|
||||||
SELECT ... -- select all columns but the one you want to remove
|
SELECT ... -- select all columns but the one you want to remove
|
||||||
@ -691,7 +694,7 @@
|
|||||||
PostgreSQL database file containing this data can be estimated as 6.4
|
PostgreSQL database file containing this data can be estimated as 6.4
|
||||||
MB:
|
MB:
|
||||||
36 bytes: each row header (approximate)
|
36 bytes: each row header (approximate)
|
||||||
24 bytes: one int field and one text filed
|
24 bytes: one int field and one text field
|
||||||
+ 4 bytes: pointer on page to tuple
|
+ 4 bytes: pointer on page to tuple
|
||||||
----------------------------------------
|
----------------------------------------
|
||||||
64 bytes per row
|
64 bytes per row
|
||||||
@ -750,7 +753,7 @@
|
|||||||
SELECT col
|
SELECT col
|
||||||
FROM tab
|
FROM tab
|
||||||
ORDER BY col [ DESC ]
|
ORDER BY col [ DESC ]
|
||||||
LIMIT 1
|
LIMIT 1;
|
||||||
|
|
||||||
When using wild-card operators such as LIKE or ~, indexes can only be
|
When using wild-card operators such as LIKE or ~, indexes can only be
|
||||||
used in certain circumstances:
|
used in certain circumstances:
|
||||||
@ -762,11 +765,11 @@
|
|||||||
|
|
||||||
The search string can not start with a character class, e.g. [a-e].
|
The search string can not start with a character class, e.g. [a-e].
|
||||||
|
|
||||||
Case-insensitive searches like ILIKE and ~* can not be used.
|
Case-insensitive searches such as ILIKE and ~* do not utilise
|
||||||
Instead, use functional indexes, which are described later in this
|
indexes. Instead, use functional indexes, which are described in
|
||||||
FAQ.
|
section 4.12.
|
||||||
|
|
||||||
The default C local must be used during initdb.
|
The default C locale must be used during initdb.
|
||||||
|
|
||||||
4.9) How do I see how the query optimizer is evaluating my query?
|
4.9) How do I see how the query optimizer is evaluating my query?
|
||||||
|
|
||||||
@ -812,11 +815,11 @@
|
|||||||
Case-insensitive equality comparisons are normally expressed as:
|
Case-insensitive equality comparisons are normally expressed as:
|
||||||
SELECT *
|
SELECT *
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE lower(col) = 'abc'
|
WHERE LOWER(col) = 'abc';
|
||||||
|
|
||||||
This will not use an standard index. However, if you create a
|
This will not use an standard index. However, if you create a
|
||||||
functional index, it will be used:
|
functional index, it will be used:
|
||||||
CREATE INDEX tabindex on tab (lower(col));
|
CREATE INDEX tabindex ON tab (LOWER(col));
|
||||||
|
|
||||||
4.13) In a query, how do I detect if a field is NULL?
|
4.13) In a query, how do I detect if a field is NULL?
|
||||||
|
|
||||||
@ -827,8 +830,8 @@
|
|||||||
Type Internal Name Notes
|
Type Internal Name Notes
|
||||||
--------------------------------------------------
|
--------------------------------------------------
|
||||||
"char" char 1 character
|
"char" char 1 character
|
||||||
CHAR(#) bpchar blank padded to the specified fixed length
|
CHAR(n) bpchar blank padded to the specified fixed length
|
||||||
VARCHAR(#) varchar size specifies maximum length, no padding
|
VARCHAR(n) varchar size specifies maximum length, no padding
|
||||||
TEXT text no specific upper limit on length
|
TEXT text no specific upper limit on length
|
||||||
BYTEA bytea variable-length byte array (null-byte safe)
|
BYTEA bytea variable-length byte array (null-byte safe)
|
||||||
|
|
||||||
@ -841,8 +844,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
data types are also subject to compression or being stored out-of-line
|
data types are also subject to compression or being stored out-of-line
|
||||||
by TOAST, so the space on disk might also be less than expected.
|
by TOAST, so the space on disk might also be less than expected.
|
||||||
|
|
||||||
CHAR() is best when storing strings that are usually the same length.
|
CHAR(n) is best when storing strings that are usually the same length.
|
||||||
VARCHAR() is best when storing variable-length strings but it limits
|
VARCHAR(n) is best when storing variable-length strings but it limits
|
||||||
how long a string can be. TEXT is for strings of unlimited length,
|
how long a string can be. TEXT is for strings of unlimited length,
|
||||||
maximum 1 gigabyte. BYTEA is for storing binary data, particularly
|
maximum 1 gigabyte. BYTEA is for storing binary data, particularly
|
||||||
values that include NULL bytes.
|
values that include NULL bytes.
|
||||||
@ -873,10 +876,10 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
|
|
||||||
One approach is to retrieve the next SERIAL value from the sequence
|
One approach is to retrieve the next SERIAL value from the sequence
|
||||||
object with the nextval() function before inserting and then insert it
|
object with the nextval() function before inserting and then insert it
|
||||||
explicitly. Using the example table in 4.15.1, that might look like
|
explicitly. Using the example table in 4.15.1, an example in a
|
||||||
this in Perl:
|
pseudo-language would look like this:
|
||||||
new_id = output of "SELECT nextval('person_id_seq')"
|
new_id = execute("SELECT nextval('person_id_seq')");
|
||||||
INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal');
|
execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
|
||||||
|
|
||||||
You would then also have the new value stored in new_id for use in
|
You would then also have the new value stored in new_id for use in
|
||||||
other queries (e.g., as a foreign key to the person table). Note that
|
other queries (e.g., as a foreign key to the person table). Note that
|
||||||
@ -886,8 +889,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
|
|
||||||
Alternatively, you could retrieve the assigned SERIAL value with the
|
Alternatively, you could retrieve the assigned SERIAL value with the
|
||||||
currval() function after it was inserted by default, e.g.,
|
currval() function after it was inserted by default, e.g.,
|
||||||
INSERT INTO person (name) VALUES ('Blaise Pascal');
|
execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
|
||||||
new_id = output of "SELECT currval('person_id_seq')";
|
new_id = execute("SELECT currval('person_id_seq')");
|
||||||
|
|
||||||
Finally, you could use the OID returned from the INSERT statement to
|
Finally, you could use the OID returned from the INSERT statement to
|
||||||
look up the default value, though this is probably the least portable
|
look up the default value, though this is probably the least portable
|
||||||
@ -898,7 +901,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
4.15.3) Don't currval() and nextval() lead to a race condition with other
|
4.15.3) Don't currval() and nextval() lead to a race condition with other
|
||||||
users?
|
users?
|
||||||
|
|
||||||
No. Currval() returns the current value assigned by your backend, not
|
No. currval() returns the current value assigned by your backend, not
|
||||||
by all users.
|
by all users.
|
||||||
|
|
||||||
4.15.4) Why aren't my sequence numbers reused on transaction abort? Why are
|
4.15.4) Why aren't my sequence numbers reused on transaction abort? Why are
|
||||||
@ -912,7 +915,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
|
|
||||||
OIDs are PostgreSQL's answer to unique row ids. Every row that is
|
OIDs are PostgreSQL's answer to unique row ids. Every row that is
|
||||||
created in PostgreSQL gets a unique OID. All OIDs generated during
|
created in PostgreSQL gets a unique OID. All OIDs generated during
|
||||||
initdb are less than 16384 (from backend/access/transam.h). All
|
initdb are less than 16384 (from include/access/transam.h). All
|
||||||
user-created OIDs are equal to or greater than this. By default, all
|
user-created OIDs are equal to or greater than this. By default, all
|
||||||
these OIDs are unique not only within a table or database, but unique
|
these OIDs are unique not only within a table or database, but unique
|
||||||
within the entire PostgreSQL installation.
|
within the entire PostgreSQL installation.
|
||||||
@ -956,7 +959,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
* range variable, table name, table alias
|
* range variable, table name, table alias
|
||||||
|
|
||||||
A list of general database terms can be found at:
|
A list of general database terms can be found at:
|
||||||
http://www.comptechnews.com/~reaster/dbdesign.html
|
http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary
|
||||||
|
/glossary.html
|
||||||
|
|
||||||
4.18) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()"?
|
4.18) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()"?
|
||||||
|
|
||||||
@ -975,7 +979,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
|
|
||||||
4.19) How do I tell what PostgreSQL version I am running?
|
4.19) How do I tell what PostgreSQL version I am running?
|
||||||
|
|
||||||
From psql, type select version();
|
From psql, type SELECT version();
|
||||||
|
|
||||||
4.20) Why does my large-object operations get "invalid large obj
|
4.20) Why does my large-object operations get "invalid large obj
|
||||||
descriptor"?
|
descriptor"?
|
||||||
@ -1004,14 +1008,14 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
|
|||||||
If the subquery returns only a few rows and the outer query returns
|
If the subquery returns only a few rows and the outer query returns
|
||||||
many rows, IN is fastest. To speed up other queries, replace IN with
|
many rows, IN is fastest. To speed up other queries, replace IN with
|
||||||
EXISTS:
|
EXISTS:
|
||||||
SELECT *
|
SELECT *
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE col IN (SELECT subcol FROM subtab)
|
WHERE col IN (SELECT subcol FROM subtab);
|
||||||
|
|
||||||
to:
|
to:
|
||||||
SELECT *
|
SELECT *
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col)
|
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
|
||||||
|
|
||||||
For this to be fast, subcol should be an indexed column. We hope to
|
For this to be fast, subcol should be an indexed column. We hope to
|
||||||
fix this limitation in a future release.
|
fix this limitation in a future release.
|
||||||
@ -1059,8 +1063,7 @@ SELECT *
|
|||||||
4.25) How do I return multiple rows or columns from a function?
|
4.25) How do I return multiple rows or columns from a function?
|
||||||
|
|
||||||
You can return result sets from PL/pgSQL functions using refcursors.
|
You can return result sets from PL/pgSQL functions using refcursors.
|
||||||
See
|
See http://www.PostgreSQL.org/idocs/index.php?plpgsql-cursors.html,
|
||||||
http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html,
|
|
||||||
section 23.7.3.3.
|
section 23.7.3.3.
|
||||||
|
|
||||||
4.26) Why can't I reliably create/drop temporary tables in PL/PgSQL
|
4.26) Why can't I reliably create/drop temporary tables in PL/PgSQL
|
||||||
@ -1079,19 +1082,19 @@ SELECT *
|
|||||||
There are several master/slave replication options available. These
|
There are several master/slave replication options available. These
|
||||||
allow only the master to make database changes and the slave can only
|
allow only the master to make database changes and the slave can only
|
||||||
do database reads. The bottom of
|
do database reads. The bottom of
|
||||||
http://gborg.postgresql.org/genpage?replication_research lists them. A
|
http://gborg.PostgreSQL.org/genpage?replication_research lists them. A
|
||||||
multi-master replication solution is being worked on at
|
multi-master replication solution is being worked on at
|
||||||
http://gborg.postgresql.org/project/pgreplication/projdisplay.php.
|
http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php.
|
||||||
|
|
||||||
4.27) What encryption options are available?
|
4.28) What encryption options are available?
|
||||||
|
|
||||||
* /contrib/pgcrypto contains many encryption functions for use in
|
* /contrib/pgcrypto contains many encryption functions for use in
|
||||||
SQL queries.
|
SQL queries.
|
||||||
* The only way to encrypt transmission from the client to the server
|
* The only way to encrypt transmission from the client to the server
|
||||||
is by using hostssl in pg_hba.conf.
|
is by using hostssl in pg_hba.conf.
|
||||||
* Database user passwords are automatically encrypted when stored in
|
* Database user passwords are automatically encrypted when stored in
|
||||||
version 7.3. In previous versions, you must enable
|
version 7.3. In previous versions, you must enable the option
|
||||||
password_encryption in postgresql.conf.
|
PASSWORD_ENCRYPTION in postgresql.conf.
|
||||||
* The server can run using an encrypted file system.
|
* The server can run using an encrypted file system.
|
||||||
_________________________________________________________________
|
_________________________________________________________________
|
||||||
|
|
||||||
|
@ -14,7 +14,7 @@
|
|||||||
alink="#0000ff">
|
alink="#0000ff">
|
||||||
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
|
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
|
||||||
|
|
||||||
<P>Last updated: Fri Oct 11 13:54:56 EDT 2002</P>
|
<P>Last updated: Sun Oct 13 22:49:56 EDT 2002</P>
|
||||||
|
|
||||||
<P>Current maintainer: Bruce Momjian (<A href=
|
<P>Current maintainer: Bruce Momjian (<A href=
|
||||||
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
|
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
|
||||||
@ -22,15 +22,14 @@
|
|||||||
|
|
||||||
<P>The most recent version of this document can be viewed at <A
|
<P>The most recent version of this document can be viewed at <A
|
||||||
href=
|
href=
|
||||||
"http://www.Postgresql.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P>
|
"http://www.PostgreSQL.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P>
|
||||||
|
|
||||||
<P>Platform-specific questions are answered at <A href=
|
<P>Platform-specific questions are answered at <A href=
|
||||||
"http://www.PostgreSQL.org/users-lounge/docs/faq.html">http://www.PostgreSQL.org/users-lounge/docs/faq.html</A>.</P>
|
"http://www.PostgreSQL.org/users-lounge/docs/faq.html">http://www.PostgreSQL.org/users-lounge/docs/faq.html</A>.</P>
|
||||||
<HR>
|
<HR>
|
||||||
|
|
||||||
<H2 align="center">General Questions</H2>
|
<H2 align="center">General Questions</H2>
|
||||||
<A href="#1.1">1.1</A>) What is PostgreSQL? How is it
|
<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR>
|
||||||
pronounced?<BR>
|
|
||||||
<A href="#1.2">1.2</A>) What is the copyright on PostgreSQL?<BR>
|
<A href="#1.2">1.2</A>) What is the copyright on PostgreSQL?<BR>
|
||||||
<A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run
|
<A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run
|
||||||
on?<BR>
|
on?<BR>
|
||||||
@ -161,7 +160,7 @@
|
|||||||
|
|
||||||
<H2 align="center">General Questions</H2>
|
<H2 align="center">General Questions</H2>
|
||||||
|
|
||||||
<H4><A name="1.1">1.1</A>) What is PostgreSQL?</H4>
|
<H4><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H4>
|
||||||
|
|
||||||
<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>.</P>
|
<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>.</P>
|
||||||
|
|
||||||
@ -172,12 +171,12 @@
|
|||||||
extended subset of <SMALL>SQL</SMALL>. PostgreSQL is free and the
|
extended subset of <SMALL>SQL</SMALL>. PostgreSQL is free and the
|
||||||
complete source is available.</P>
|
complete source is available.</P>
|
||||||
|
|
||||||
<P>PostgreSQL development is performed by a team of Internet
|
<P>PostgreSQL development is performed by a team of
|
||||||
developers who all subscribe to the PostgreSQL development mailing
|
developers who all subscribe to the PostgreSQL development mailing
|
||||||
list. The current coordinator is Marc G. Fournier (<A href=
|
list. The current coordinator is Marc G. Fournier (<A href=
|
||||||
"mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See
|
"mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See
|
||||||
below on how to join). This team is now responsible for all
|
section <a href="#1.6">1.6</a> on how to join). This team is now
|
||||||
development of PostgreSQL.</P>
|
responsible for all development of PostgreSQL.</P>
|
||||||
|
|
||||||
<P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen.
|
<P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen.
|
||||||
Many others have contributed to the porting, testing, debugging,
|
Many others have contributed to the porting, testing, debugging,
|
||||||
@ -239,10 +238,10 @@
|
|||||||
<P><STRONG>Client</STRONG></P>
|
<P><STRONG>Client</STRONG></P>
|
||||||
|
|
||||||
<P>It is possible to compile the <I>libpq</I> C library, psql, and
|
<P>It is possible to compile the <I>libpq</I> C library, psql, and
|
||||||
other interfaces and binaries to run on MS Windows platforms. In
|
other interfaces and client applications to run on MS Windows platforms.
|
||||||
this case, the client is running on MS Windows, and communicates
|
In this case, the client is running on MS Windows, and communicates
|
||||||
via TCP/IP to a server running on one of our supported Unix
|
via TCP/IP to a server running on one of our supported Unix
|
||||||
platforms. A file <I>win31.mak</I> is included in the distribution
|
platforms. A file <I>win32.mak</I> is included in the distribution
|
||||||
for making a Win32 <I>libpq</I> library and <I>psql</I>. PostgreSQL
|
for making a Win32 <I>libpq</I> library and <I>psql</I>. PostgreSQL
|
||||||
also communicates with <SMALL>ODBC</SMALL> clients.</P>
|
also communicates with <SMALL>ODBC</SMALL> clients.</P>
|
||||||
|
|
||||||
@ -250,10 +249,11 @@
|
|||||||
|
|
||||||
<P>The database server can run on Windows NT and Win2k using
|
<P>The database server can run on Windows NT and Win2k using
|
||||||
Cygwin, the Cygnus Unix/NT porting library. See
|
Cygwin, the Cygnus Unix/NT porting library. See
|
||||||
<I>pgsql/doc/FAQ_MSWIN</I> in the distribution or the <A href=
|
<I>pgsql/doc/FAQ_MSWIN</I> in the distribution or the MS Windows FAQ
|
||||||
"http://www.postgresql.org/docs/faq-mswin.html">MS Windows FAQ</A>
|
at <A href="http://www.PostgreSQL.org/docs/faq-mswin.html">http://www.PostgreSQL.org/docs/faq-mswin.html</A>.</P>
|
||||||
on our web site. We have no plan to do a native port to any
|
|
||||||
Microsoft platform.</P>
|
<p>A native port to some Microsoft platforms is currently being worked
|
||||||
|
upon.</p>
|
||||||
|
|
||||||
<H4><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H4>
|
<H4><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H4>
|
||||||
|
|
||||||
@ -318,7 +318,7 @@
|
|||||||
'#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P>
|
'#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P>
|
||||||
|
|
||||||
<P>A list of commercial support companies is available at <A href=
|
<P>A list of commercial support companies is available at <A href=
|
||||||
"http://www.postgresql.org/users-lounge/commercial-support.html">http://www.postgresql.org/users-lounge/commercial-support.html</A>.</P>
|
"http://www.PostgreSQL.org/users-lounge/commercial-support.html">http://www.PostgreSQL.org/users-lounge/commercial-support.html</A>.</P>
|
||||||
|
|
||||||
<H4><A name="1.7">1.7</A>) What is the latest release?</H4>
|
<H4><A name="1.7">1.7</A>) What is the latest release?</H4>
|
||||||
|
|
||||||
@ -339,10 +339,10 @@
|
|||||||
"http://www.commandprompt.com/ppbook/">http://www.commandprompt.com/ppbook/</A>.
|
"http://www.commandprompt.com/ppbook/">http://www.commandprompt.com/ppbook/</A>.
|
||||||
There is a list of PostgreSQL books available for purchase at <A
|
There is a list of PostgreSQL books available for purchase at <A
|
||||||
href=
|
href=
|
||||||
"http://www.postgresql.org/books/">http://www.postgresql.org/books/</A>.
|
"http://www.ca.PostgreSQL.org/books/">http://www.ca.PostgreSQL.org/books/</A>.
|
||||||
There is also a collection of PostgreSQL technical articles at <A
|
There is also a collection of PostgreSQL technical articles at <A
|
||||||
href=
|
href=
|
||||||
"http://techdocs.postgresql.org/">http://techdocs.postgresql.org/</A>.</P>
|
"http://techdocs.PostgreSQL.org/">http://techdocs.PostgreSQL.org/</A>.</P>
|
||||||
|
|
||||||
<P><I>psql</I> has some nice \d commands to show information about
|
<P><I>psql</I> has some nice \d commands to show information about
|
||||||
types, operators, functions, aggregates, etc.</P>
|
types, operators, functions, aggregates, etc.</P>
|
||||||
@ -402,10 +402,10 @@
|
|||||||
|
|
||||||
<H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4>
|
<H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4>
|
||||||
|
|
||||||
<P>Please visit the <A href=
|
<P>Please visit the PostgreSQL BugTool page at <A href=
|
||||||
"http://www.postgresql.org/bugs/bugs.php">PostgreSQL BugTool</A>
|
"http://www.PostgreSQL.org/bugs/bugs.php">http://www.PostgreSQL.org/bugs/bugs.php</A>,
|
||||||
page, which gives guidelines and directions on how to submit a
|
which gives guidelines and directions on how to submit a
|
||||||
bug.</P>
|
bug report.</P>
|
||||||
|
|
||||||
<P>Also check out our ftp site <A href=
|
<P>Also check out our ftp site <A href=
|
||||||
"ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to
|
"ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to
|
||||||
@ -460,14 +460,14 @@
|
|||||||
|
|
||||||
<DT><B>Support</B></DT>
|
<DT><B>Support</B></DT>
|
||||||
|
|
||||||
<DD>Our mailing list provides a large group of developers and
|
<DD>Our mailing lists provide contact with a large group of developers
|
||||||
users to help resolve any problems encountered. While we can not
|
and users to help resolve any problems encountered. While we cannot
|
||||||
guarantee a fix, commercial <SMALL>DBMS</SMALL>s do not always
|
guarantee a fix, commercial <SMALL>DBMS</SMALL>s do not always
|
||||||
supply a fix either. Direct access to developers, the user
|
supply a fix either. Direct access to developers, the user
|
||||||
community, manuals, and the source code often make PostgreSQL
|
community, manuals, and the source code often make PostgreSQL
|
||||||
support superior to other <SMALL>DBMS</SMALL>s. There is
|
support superior to other <SMALL>DBMS</SMALL>s. There is
|
||||||
commercial per-incident support available for those who need it.
|
commercial per-incident support available for those who need it.
|
||||||
(See <A href="#1.6">support FAQ item</A>.)<BR>
|
(See <A href="#1.6">FAQ section 1.6</A>.)<BR>
|
||||||
<BR>
|
<BR>
|
||||||
</DD>
|
</DD>
|
||||||
|
|
||||||
@ -484,7 +484,7 @@
|
|||||||
PostgreSQL?</H4>
|
PostgreSQL?</H4>
|
||||||
|
|
||||||
<P>PostgreSQL has had a first-class infrastructure since we started
|
<P>PostgreSQL has had a first-class infrastructure since we started
|
||||||
six years ago. This is all thanks to Marc Fournier, who has created
|
in 1994. This is all thanks to Marc Fournier, who has created
|
||||||
and managed this infrastructure over the years.</P>
|
and managed this infrastructure over the years.</P>
|
||||||
|
|
||||||
<P>Quality infrastructure is very important to an open-source
|
<P>Quality infrastructure is very important to an open-source
|
||||||
@ -494,9 +494,7 @@
|
|||||||
<P>Of course, this infrastructure is not cheap. There are a variety
|
<P>Of course, this infrastructure is not cheap. There are a variety
|
||||||
of monthly and one-time expenses that are required to keep it
|
of monthly and one-time expenses that are required to keep it
|
||||||
going. If you or your company has money it can donate to help fund
|
going. If you or your company has money it can donate to help fund
|
||||||
this effort, please go to <A href=
|
this effort, please go to <A href="http://store.pgsql.com/shopping/">http://store.pgsql.com/shopping/</A>
|
||||||
"https://store.pgsql.com/shopping/index.php?id=1">
|
|
||||||
https://store.pgsql.com/shopping/index.php?id=1</A>
|
|
||||||
and make a donation.</P>
|
and make a donation.</P>
|
||||||
|
|
||||||
<P>Although the web page mentions PostgreSQL, Inc, the
|
<P>Although the web page mentions PostgreSQL, Inc, the
|
||||||
@ -538,28 +536,23 @@
|
|||||||
<P>A nice introduction to Database-backed Web pages can be seen at:
|
<P>A nice introduction to Database-backed Web pages can be seen at:
|
||||||
<A href="http://www.webreview.com">http://www.webreview.com</A></P>
|
<A href="http://www.webreview.com">http://www.webreview.com</A></P>
|
||||||
|
|
||||||
<P>There is also one at <A href=
|
|
||||||
"http://www.phone.net/home/mwm/hotlist/">http://www.phone.net/home/mwm/hotlist/.</A></P>
|
|
||||||
|
|
||||||
<P>For Web integration, PHP is an excellent interface. It is at <A
|
<P>For Web integration, PHP is an excellent interface. It is at <A
|
||||||
href="http://www.php.net">http://www.php.net</A>.</P>
|
href="http://www.php.net">http://www.php.net</A>.</P>
|
||||||
|
|
||||||
<P>For complex cases, many use the Perl interface and CGI.pm.</P>
|
<P>For complex cases, many use the Perl interface and CGI.pm or mod_perl.</P>
|
||||||
|
|
||||||
<H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user
|
<H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user
|
||||||
interface? A report generator? An embedded query language
|
interface? A report generator? An embedded query language
|
||||||
interface?</H4>
|
interface?</H4>
|
||||||
|
|
||||||
<P>We have a nice graphical user interface called <I>pgaccess</I>,
|
<P>We have a nice graphical user interface called PgAccess, which is
|
||||||
which is shipped as part of the distribution. <I>pgaccess</I> also
|
shipped as part of the distribution. PgAccess also has a report
|
||||||
has a report generator. The Web page is <A href=
|
generator. The Web page is <A href="http://www.pgaccess.org/">http://www.pgaccess.org/</A>.</P>
|
||||||
"http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A></P>
|
|
||||||
|
|
||||||
<P>We also include <I>ecpg</I>, which is an embedded SQL query
|
<P>We also include <I>ecpg</I>, which is an embedded SQL query
|
||||||
language interface for C.</P>
|
language interface for C.</P>
|
||||||
|
|
||||||
<H4><A name="2.4">2.4</A>) What languages are available to
|
<H4><A name="2.4">2.4</A>) What languages are able to communicate with PostgreSQL?</H4>
|
||||||
communicate with PostgreSQL?</H4>
|
|
||||||
|
|
||||||
<P>We have:</P>
|
<P>We have:</P>
|
||||||
|
|
||||||
@ -572,7 +565,7 @@
|
|||||||
|
|
||||||
<LI>Java (jdbc)</LI>
|
<LI>Java (jdbc)</LI>
|
||||||
|
|
||||||
<LI>Perl (perl5)</LI>
|
<LI>Perl (DBD::Pg)</LI>
|
||||||
|
|
||||||
<LI>ODBC (odbc)</LI>
|
<LI>ODBC (odbc)</LI>
|
||||||
|
|
||||||
@ -582,12 +575,10 @@
|
|||||||
|
|
||||||
<LI>C Easy API (libpgeasy)</LI>
|
<LI>C Easy API (libpgeasy)</LI>
|
||||||
|
|
||||||
<LI>Embedded <SMALL>HTML</SMALL> (<A href=
|
<LI>PHP ('pg_' functions, Pear::DB)</LI>
|
||||||
"http://www.php.net">PHP from http://www.php.net</A>)</LI>
|
|
||||||
</UL>
|
</UL>
|
||||||
<P>Additional interfaces are available at <a
|
<P>Additional interfaces are available at
|
||||||
href="http://www.postgresql.org/interfaces.html">
|
<a href="http://www.PostgreSQL.org/interfaces.html">http://www.PostgreSQL.org/interfaces.html</A>.
|
||||||
http://www.postgresql.org/interfaces.html.</A>
|
|
||||||
</P>
|
</P>
|
||||||
<HR>
|
<HR>
|
||||||
|
|
||||||
@ -774,7 +765,7 @@
|
|||||||
the MaxBackendId constant in
|
the MaxBackendId constant in
|
||||||
<I>include/storage/sinvaladt.h</I>.</P>
|
<I>include/storage/sinvaladt.h</I>.</P>
|
||||||
|
|
||||||
<H4><A name="3.9">3.9</A>) What are the <I>pg_sorttempNNN.NN</I>
|
<H4><A name="3.9">3.9</A>) What are the <I>pg_tempNNN.NN</I>
|
||||||
files in my database directory?</H4>
|
files in my database directory?</H4>
|
||||||
|
|
||||||
<P>They are temporary files generated by the query executor. For
|
<P>They are temporary files generated by the query executor. For
|
||||||
@ -793,16 +784,16 @@
|
|||||||
|
|
||||||
<P>The PostgreSQL team makes only small changes between minor releases,
|
<P>The PostgreSQL team makes only small changes between minor releases,
|
||||||
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
||||||
However, major releases often change the internal format of system
|
However, major releases (e.g. from 7.2 to 7.3) often change the internal
|
||||||
tables and data files. These changes are often complex, so we don't
|
format of system tables and data files. These changes are often complex,
|
||||||
maintain backward compatability for data files. A dump outputs data
|
so we don't maintain backward compatability for data files. A dump outputs
|
||||||
in a generic format that can then be loaded in using the new internal
|
data in a generic format that can then be loaded in using the new internal
|
||||||
format.
|
format.</P>
|
||||||
|
|
||||||
<P>In releases where the on-disk format does not change, the
|
<p>In releases where the on-disk format does not change, the
|
||||||
<i>pg_upgrade</i> script can be used to upgrade without a dump/restore.
|
<i>pg_upgrade</i> script can be used to upgrade without a dump/restore.
|
||||||
The release notes mention whether <i>pg_upgrade</i> is available for the
|
The release notes mention whether <i>pg_upgrade</i> is available for the
|
||||||
release.
|
release.</p>
|
||||||
|
|
||||||
<HR>
|
<HR>
|
||||||
|
|
||||||
@ -821,7 +812,7 @@
|
|||||||
<SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P>
|
<SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P>
|
||||||
|
|
||||||
<P>The entire query may have to be evaluated, even if you only want
|
<P>The entire query may have to be evaluated, even if you only want
|
||||||
the first few rows. Consider a query that has an <SMALL>ORDER
|
the first few rows. Consider using a query that has an <SMALL>ORDER
|
||||||
BY.</SMALL> If there is an index that matches the <SMALL>ORDER
|
BY.</SMALL> If there is an index that matches the <SMALL>ORDER
|
||||||
BY</SMALL>, PostgreSQL may be able to evaluate only the first few
|
BY</SMALL>, PostgreSQL may be able to evaluate only the first few
|
||||||
records requested, or the entire query may have to be evaluated
|
records requested, or the entire query may have to be evaluated
|
||||||
@ -840,8 +831,8 @@
|
|||||||
<H4><A name="4.4">4.4</A>) How do you remove a column from a
|
<H4><A name="4.4">4.4</A>) How do you remove a column from a
|
||||||
table?</H4>
|
table?</H4>
|
||||||
|
|
||||||
<P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
|
<P>Prior to version 7.3, <SMALL>ALTER TABLE DROP COLUMN</SMALL> is not supported.
|
||||||
this:</P>
|
You can do this instead:</P>
|
||||||
<PRE>
|
<PRE>
|
||||||
BEGIN;
|
BEGIN;
|
||||||
LOCK TABLE old_table;
|
LOCK TABLE old_table;
|
||||||
@ -892,7 +883,7 @@
|
|||||||
be estimated as 6.4 MB:</P>
|
be estimated as 6.4 MB:</P>
|
||||||
<PRE>
|
<PRE>
|
||||||
36 bytes: each row header (approximate)
|
36 bytes: each row header (approximate)
|
||||||
24 bytes: one int field and one text filed
|
24 bytes: one int field and one text field
|
||||||
+ 4 bytes: pointer on page to tuple
|
+ 4 bytes: pointer on page to tuple
|
||||||
----------------------------------------
|
----------------------------------------
|
||||||
64 bytes per row
|
64 bytes per row
|
||||||
@ -957,7 +948,7 @@
|
|||||||
SELECT col
|
SELECT col
|
||||||
FROM tab
|
FROM tab
|
||||||
ORDER BY col [ DESC ]
|
ORDER BY col [ DESC ]
|
||||||
LIMIT 1
|
LIMIT 1;
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or
|
<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or
|
||||||
@ -972,10 +963,10 @@
|
|||||||
</UL>
|
</UL>
|
||||||
<LI>The search string can not start with a character class,
|
<LI>The search string can not start with a character class,
|
||||||
e.g. [a-e].</LI>
|
e.g. [a-e].</LI>
|
||||||
<LI>Case-insensitive searches like <SMALL>ILIKE</SMALL> and
|
<LI>Case-insensitive searches such as <SMALL>ILIKE</SMALL> and
|
||||||
<I>~*</I> can not be used. Instead, use functional
|
<I>~*</I> do not utilise indexes. Instead, use functional
|
||||||
indexes, which are described later in this FAQ.</LI>
|
indexes, which are described in section <a href="#4.12">4.12</a>.</LI>
|
||||||
<LI>The default <I>C</I> local must be used during
|
<LI>The default <I>C</I> locale must be used during
|
||||||
<i>initdb.</i></LI>
|
<i>initdb.</i></LI>
|
||||||
</UL>
|
</UL>
|
||||||
<P>
|
<P>
|
||||||
@ -1032,13 +1023,13 @@
|
|||||||
<PRE>
|
<PRE>
|
||||||
SELECT *
|
SELECT *
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE lower(col) = 'abc'
|
WHERE LOWER(col) = 'abc';
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
This will not use an standard index. However, if you create a
|
This will not use an standard index. However, if you create a
|
||||||
functional index, it will be used:
|
functional index, it will be used:
|
||||||
<PRE>
|
<PRE>
|
||||||
CREATE INDEX tabindex on tab (lower(col));
|
CREATE INDEX tabindex ON tab (LOWER(col));
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
<H4><A name="4.13">4.13</A>) In a query, how do I detect if a field
|
<H4><A name="4.13">4.13</A>) In a query, how do I detect if a field
|
||||||
@ -1053,8 +1044,8 @@
|
|||||||
Type Internal Name Notes
|
Type Internal Name Notes
|
||||||
--------------------------------------------------
|
--------------------------------------------------
|
||||||
"char" char 1 character
|
"char" char 1 character
|
||||||
CHAR(#) bpchar blank padded to the specified fixed length
|
CHAR(n) bpchar blank padded to the specified fixed length
|
||||||
VARCHAR(#) varchar size specifies maximum length, no padding
|
VARCHAR(n) varchar size specifies maximum length, no padding
|
||||||
TEXT text no specific upper limit on length
|
TEXT text no specific upper limit on length
|
||||||
BYTEA bytea variable-length byte array (null-byte safe)
|
BYTEA bytea variable-length byte array (null-byte safe)
|
||||||
</PRE>
|
</PRE>
|
||||||
@ -1069,8 +1060,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
stored out-of-line by <SMALL>TOAST</SMALL>, so the space on disk
|
stored out-of-line by <SMALL>TOAST</SMALL>, so the space on disk
|
||||||
might also be less than expected.</P>
|
might also be less than expected.</P>
|
||||||
|
|
||||||
<P><SMALL>CHAR()</SMALL> is best when storing strings that are
|
<P><SMALL>CHAR(n)</SMALL> is best when storing strings that are
|
||||||
usually the same length. <SMALL>VARCHAR()</SMALL> is best when
|
usually the same length. <SMALL>VARCHAR(n)</SMALL> is best when
|
||||||
storing variable-length strings but it limits how long a string can
|
storing variable-length strings but it limits how long a string can
|
||||||
be. <SMALL>TEXT</SMALL> is for strings of unlimited length, maximum
|
be. <SMALL>TEXT</SMALL> is for strings of unlimited length, maximum
|
||||||
1 gigabyte. <SMALL>BYTEA</SMALL> is for storing binary data,
|
1 gigabyte. <SMALL>BYTEA</SMALL> is for storing binary data,
|
||||||
@ -1111,11 +1102,11 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
<P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value
|
<P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value
|
||||||
from the sequence object with the <I>nextval()</I> function
|
from the sequence object with the <I>nextval()</I> function
|
||||||
<I>before</I> inserting and then insert it explicitly. Using the
|
<I>before</I> inserting and then insert it explicitly. Using the
|
||||||
example table in <A href="#4.15.1">4.15.1</A>, that might look like
|
example table in <A href="#4.15.1">4.15.1</A>, an example in a
|
||||||
this in Perl:</P>
|
pseudo-language would look like this:</P>
|
||||||
<PRE>
|
<PRE>
|
||||||
new_id = output of "SELECT nextval('person_id_seq')"
|
new_id = execute("SELECT nextval('person_id_seq')");
|
||||||
INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal');
|
execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
You would then also have the new value stored in
|
You would then also have the new value stored in
|
||||||
@ -1124,14 +1115,14 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
automatically created <SMALL>SEQUENCE</SMALL> object will be named
|
automatically created <SMALL>SEQUENCE</SMALL> object will be named
|
||||||
<<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where
|
<<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where
|
||||||
<I>table</I> and <I>serialcolumn</I> are the names of your table
|
<I>table</I> and <I>serialcolumn</I> are the names of your table
|
||||||
and your <SMALL>SERIAL</SMALL> column, respectively.
|
and your <SMALL>SERIAL</SMALL> column, respectively.
|
||||||
|
|
||||||
<P>Alternatively, you could retrieve the assigned
|
<P>Alternatively, you could retrieve the assigned
|
||||||
<SMALL>SERIAL</SMALL> value with the <I>currval</I>() function
|
<SMALL>SERIAL</SMALL> value with the <I>currval</I>() function
|
||||||
<I>after</I> it was inserted by default, e.g.,</P>
|
<I>after</I> it was inserted by default, e.g.,</P>
|
||||||
<PRE>
|
<PRE>
|
||||||
INSERT INTO person (name) VALUES ('Blaise Pascal');
|
execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
|
||||||
new_id = output of "SELECT currval('person_id_seq')";
|
new_id = execute("SELECT currval('person_id_seq')");
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A>
|
Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A>
|
||||||
@ -1139,12 +1130,12 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
default value, though this is probably the least portable approach.
|
default value, though this is probably the least portable approach.
|
||||||
In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid
|
In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid
|
||||||
value is made available via <I>$sth->{pg_oid_status}</I> after
|
value is made available via <I>$sth->{pg_oid_status}</I> after
|
||||||
<I>$sth->execute()</I>.
|
<I>$sth->execute()</I>.
|
||||||
|
|
||||||
<H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and
|
<H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and
|
||||||
<I>nextval()</I> lead to a race condition with other users?</H4>
|
<I>nextval()</I> lead to a race condition with other users?</H4>
|
||||||
|
|
||||||
<P>No. Currval() returns the current value assigned by your
|
<P>No. <i>currval</i>() returns the current value assigned by your
|
||||||
backend, not by all users.</P>
|
backend, not by all users.</P>
|
||||||
|
|
||||||
<H4><A name="4.15.4">4.15.4</A>) Why aren't my sequence numbers
|
<H4><A name="4.15.4">4.15.4</A>) Why aren't my sequence numbers
|
||||||
@ -1163,7 +1154,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
Every row that is created in PostgreSQL gets a unique
|
Every row that is created in PostgreSQL gets a unique
|
||||||
<SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during
|
<SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during
|
||||||
<I>initdb</I> are less than 16384 (from
|
<I>initdb</I> are less than 16384 (from
|
||||||
<I>backend/access/transam.h</I>). All user-created
|
<I>include/access/transam.h</I>). All user-created
|
||||||
<SMALL>OID</SMALL>s are equal to or greater than this. By default,
|
<SMALL>OID</SMALL>s are equal to or greater than this. By default,
|
||||||
all these <SMALL>OID</SMALL>s are unique not only within a table or
|
all these <SMALL>OID</SMALL>s are unique not only within a table or
|
||||||
database, but unique within the entire PostgreSQL installation.</P>
|
database, but unique within the entire PostgreSQL installation.</P>
|
||||||
@ -1186,12 +1177,11 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
COPY new TO '/tmp/pgtable';
|
COPY new TO '/tmp/pgtable';
|
||||||
DELETE FROM new;
|
DELETE FROM new;
|
||||||
COPY new WITH OIDS FROM '/tmp/pgtable';
|
COPY new WITH OIDS FROM '/tmp/pgtable';
|
||||||
|
</PRE>
|
||||||
<!--
|
<!--
|
||||||
CREATE TABLE new_table (mycol int);
|
CREATE TABLE new_table (mycol int);
|
||||||
INSERT INTO new_table (oid, mycol) SELECT oid, mycol FROM old_table;
|
INSERT INTO new_table (oid, mycol) SELECT oid, mycol FROM old_table;
|
||||||
-->
|
-->
|
||||||
</PRE>
|
|
||||||
|
|
||||||
<P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will
|
<P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will
|
||||||
overflow at 4 billion. No one has reported this ever happening, and
|
overflow at 4 billion. No one has reported this ever happening, and
|
||||||
we plan to have the limit removed before anyone does.</P>
|
we plan to have the limit removed before anyone does.</P>
|
||||||
@ -1228,7 +1218,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
</UL>
|
</UL>
|
||||||
|
|
||||||
<P>A list of general database terms can be found at: <A href=
|
<P>A list of general database terms can be found at: <A href=
|
||||||
"http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
|
"http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html">http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html</A></P>
|
||||||
|
|
||||||
<H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR:
|
<H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR:
|
||||||
Memory exhausted in AllocSetAlloc()"</I>?</H4>
|
Memory exhausted in AllocSetAlloc()"</I>?</H4>
|
||||||
@ -1247,12 +1237,12 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
and all subprocesses created after the command is run. If you are
|
and all subprocesses created after the command is run. If you are
|
||||||
having a problem with the <SMALL>SQL</SMALL> client because the
|
having a problem with the <SMALL>SQL</SMALL> client because the
|
||||||
backend is returning too much data, try it before starting the
|
backend is returning too much data, try it before starting the
|
||||||
client.
|
client.
|
||||||
|
|
||||||
<H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version
|
<H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version
|
||||||
I am running?</H4>
|
I am running?</H4>
|
||||||
|
|
||||||
<P>From <I>psql</I>, type <CODE>select version();</CODE></P>
|
<P>From <I>psql</I>, type <CODE>SELECT version();</CODE></P>
|
||||||
|
|
||||||
<H4><A name="4.20">4.20</A>) Why does my large-object operations
|
<H4><A name="4.20">4.20</A>) Why does my large-object operations
|
||||||
get <I>"invalid large obj descriptor"</I>?</H4>
|
get <I>"invalid large obj descriptor"</I>?</H4>
|
||||||
@ -1288,22 +1278,18 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
returns many rows, <CODE><SMALL>IN</SMALL></CODE> is fastest. To
|
returns many rows, <CODE><SMALL>IN</SMALL></CODE> is fastest. To
|
||||||
speed up other queries, replace <CODE>IN</CODE> with
|
speed up other queries, replace <CODE>IN</CODE> with
|
||||||
<CODE>EXISTS</CODE>:</P>
|
<CODE>EXISTS</CODE>:</P>
|
||||||
<PRE>
|
<PRE> SELECT *
|
||||||
<CODE>SELECT *
|
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE col IN (SELECT subcol FROM subtab)
|
WHERE col IN (SELECT subcol FROM subtab);
|
||||||
</CODE>
|
|
||||||
</PRE>
|
</PRE>
|
||||||
to:
|
to:
|
||||||
<PRE>
|
<PRE> SELECT *
|
||||||
<CODE>SELECT *
|
|
||||||
FROM tab
|
FROM tab
|
||||||
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col)
|
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
|
||||||
</CODE>
|
|
||||||
</PRE>
|
</PRE>
|
||||||
|
|
||||||
For this to be fast, <CODE>subcol</CODE> should be an indexed column.
|
For this to be fast, <CODE>subcol</CODE> should be an indexed column.
|
||||||
We hope to fix this limitation in a future release.
|
We hope to fix this limitation in a future release.
|
||||||
|
|
||||||
<H4><A name="4.23">4.23</A>) How do I perform an outer join?</H4>
|
<H4><A name="4.23">4.23</A>) How do I perform an outer join?</H4>
|
||||||
|
|
||||||
@ -1362,8 +1348,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
|
|
||||||
<P>You can return result sets from PL/pgSQL functions using
|
<P>You can return result sets from PL/pgSQL functions using
|
||||||
<I>refcursors</I>. See <A href=
|
<I>refcursors</I>. See <A href=
|
||||||
"http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html">
|
"http://www.PostgreSQL.org/idocs/index.php?plpgsql-cursors.html">
|
||||||
http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html,</A>
|
http://www.PostgreSQL.org/idocs/index.php?plpgsql-cursors.html</A>,
|
||||||
section 23.7.3.3.</P>
|
section 23.7.3.3.</P>
|
||||||
|
|
||||||
<H4><A name="4.26">4.26</A>) Why can't I reliably create/drop
|
<H4><A name="4.26">4.26</A>) Why can't I reliably create/drop
|
||||||
@ -1381,13 +1367,12 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
<P>There are several master/slave replication options available.
|
<P>There are several master/slave replication options available.
|
||||||
These allow only the master to make database changes and the slave
|
These allow only the master to make database changes and the slave
|
||||||
can only do database reads. The bottom of <a
|
can only do database reads. The bottom of <a
|
||||||
href="http://gborg.postgresql.org/genpage?replication_research">
|
href="http://gborg.PostgreSQL.org/genpage?replication_research">
|
||||||
http://gborg.postgresql.org/genpage?replication_research</a> lists
|
http://gborg.PostgreSQL.org/genpage?replication_research</a> lists
|
||||||
them. A multi-master replication solution is being worked on at <a
|
them. A multi-master replication solution is being worked on at <a
|
||||||
href="http://gborg.postgresql.org/project/pgreplication/projdisplay.
|
href="http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php">http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php</a>.</P>
|
||||||
php">http://gborg.postgresql.org/project/pgreplication/projdisplay.php</a>.</P>
|
|
||||||
|
|
||||||
<H4><A name="4.27">4.27</A>) What encryption options are available?
|
<H4><A name="4.28">4.28</A>) What encryption options are available?
|
||||||
</H4>
|
</H4>
|
||||||
<UL>
|
<UL>
|
||||||
<LI><I>/contrib/pgcrypto</I> contains many encryption functions for
|
<LI><I>/contrib/pgcrypto</I> contains many encryption functions for
|
||||||
@ -1395,8 +1380,8 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
|||||||
<LI>The only way to encrypt transmission from the client to the
|
<LI>The only way to encrypt transmission from the client to the
|
||||||
server is by using <I>hostssl</I> in <I>pg_hba.conf</I>.</LI>
|
server is by using <I>hostssl</I> in <I>pg_hba.conf</I>.</LI>
|
||||||
<LI>Database user passwords are automatically encrypted when stored
|
<LI>Database user passwords are automatically encrypted when stored
|
||||||
in version 7.3. In previous versions, you must enable
|
in version 7.3. In previous versions, you must enable the option
|
||||||
<I>password_encryption</I> in <I>postgresql.conf</I>.</LI>
|
<i>PASSWORD_ENCRYPTION</i> in <i>postgresql.conf</i>.</LI>
|
||||||
<LI>The server can run using an encrypted file system.</LI>
|
<LI>The server can run using an encrypted file system.</LI>
|
||||||
</UL>
|
</UL>
|
||||||
|
|
||||||
|
Loading…
x
Reference in New Issue
Block a user