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Patches for the SGML documentation relating

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to the tutorial code changes.

NOTE:  I couldn't get ngsmls to find the document
type so that the changes could be checked.  However,
the changes were very minor:

Best,

Clark
This commit is contained in:
Bruce Momjian 1999-03-14 15:24:15 +00:00
parent 344190b7ef
commit f45ec44c6b
1 changed files with 133 additions and 93 deletions
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216
doc/src/sgml/xfunc.sgml
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@ -7,19 +7,20 @@
Consequently, while it is possible to define a new Consequently, while it is possible to define a new
function without defining a new type, the reverse is function without defining a new type, the reverse is
not true. We therefore describe how to add new functions not true. We therefore describe how to add new functions
to <ProductName>Postgres</ProductName> before describing how to add new to <ProductName>Postgres</ProductName> before describing
types. how to add new types.
<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym> provides two types of functions: query <ProductName>Postgres</ProductName> <Acronym>SQL</Acronym>
language functions (functions written in <Acronym>SQL</Acronym> and provides two types of functions: query language functions
programming language functions (functions written in a (functions written in <Acronym>SQL</Acronym> and programming
compiled programming language such as <Acronym>C</Acronym>.) Either kind language functions (functions written in a compiled
programming language such as <Acronym>C</Acronym>.) Either kind
of function can take a base type, a composite type or of function can take a base type, a composite type or
some combination as arguments (parameters). In addition, some combination as arguments (parameters). In addition,
both kinds of functions can return a base type or both kinds of functions can return a base type or
a composite type. It's easier to define <Acronym>SQL</Acronym> functions, a composite type. It's easier to define <Acronym>SQL</Acronym>
so we'll start with those. functions, so we'll start with those. Examples in this section
Examples in this section can also be found in <FileName>funcs.sql</FileName> can also be found in <FileName>funcs.sql</FileName>
and <FileName>C-code/funcs.c</FileName>. and <FileName>funcs.c</FileName>.
</Para> </Para>
<Sect1> <Sect1>
@ -54,8 +55,8 @@
instead of one. instead of one.
</Para> </Para>
<Para> <Para>
It's almost as easy to define <Acronym>SQL</Acronym> functions that take It's almost as easy to define <Acronym>SQL</Acronym> functions
base types as arguments. In the example below, notice that take base types as arguments. In the example below, notice
how we refer to the arguments within the function as $1 how we refer to the arguments within the function as $1
and $2. and $2.
@ -91,7 +92,8 @@
SELECT name, double_salary(EMP) AS dream SELECT name, double_salary(EMP) AS dream
FROM EMP FROM EMP
WHERE EMP.dept = 'toy'; WHERE EMP.cubicle ~= '(2,1)'::point;
+-----+-------+ +-----+-------+
|name | dream | |name | dream |
@ -137,7 +139,7 @@
AS 'SELECT \'None\'::text AS name, AS 'SELECT \'None\'::text AS name,
1000 AS salary, 1000 AS salary,
25 AS age, 25 AS age,
\'none\'::text AS dept;' \'(2,2)\'::point AS cubicle'
LANGUAGE 'sql'; LANGUAGE 'sql';
</ProgramListing> </ProgramListing>
@ -153,15 +155,15 @@
<ItemizedList> <ItemizedList>
<ListItem> <ListItem>
<Para> <Para>
The target list order must be exactly the same as The target list order must be exactly the same as
that in which the attributes appear in the CREATE that in which the attributes appear in the CREATE
TABLE statement (or when you execute a .* query). TABLE statement (or when you execute a .* query).
</Para> </Para>
</ListItem> </ListItem>
<ListItem> <ListItem>
<Para> <Para>
You must typecast the expressions You must typecast the expressions (using ::) very carefully
(using ::) very carefully or you will see the following error: or you will see the following error:
<ProgramListing> <ProgramListing>
WARN::function declared to return type EMP does not retrieve (EMP.*) WARN::function declared to return type EMP does not retrieve (EMP.*)
@ -202,11 +204,12 @@ The reason why, in general, we must use the function
</ItemizedList> </ItemizedList>
</para> </para>
<Para> <Para>
Any collection of commands in the <Acronym>SQL</Acronym> query language Any collection of commands in the <Acronym>SQL</Acronym> query
can be packaged together and defined as a function. language can be packaged together and defined as a function.
The commands can include updates (i.e., <Acronym>insert</Acronym>, <Acronym>update</Acronym> The commands can include updates (i.e., <Acronym>insert</Acronym>,
and <Acronym>delete</Acronym>) as well as <Acronym>select</Acronym> queries. However, the <Acronym>update</Acronym> and <Acronym>delete</Acronym>) as well
final command must be a <Acronym>select</Acronym> that returns whatever is as <Acronym>select</Acronym> queries. However, the final command
must be a <Acronym>select</Acronym> that returns whatever is
specified as the function's returntype. specified as the function's returntype.
<ProgramListing> <ProgramListing>
@ -222,6 +225,7 @@ The reason why, in general, we must use the function
+--+ +--+
|1 | |1 |
+--+ +--+
</ProgramListing> </ProgramListing>
</Para> </Para>
</sect2> </sect2>
@ -234,12 +238,13 @@ The reason why, in general, we must use the function
<Title>Programming Language Functions on Base Types</Title> <Title>Programming Language Functions on Base Types</Title>
<Para> <Para>
Internally, <ProductName>Postgres</ProductName> regards a base type as a "blob of Internally, <ProductName>Postgres</ProductName> regards a
memory." The user-defined functions that you define base type as a "blob of memory." The user-defined
over a type in turn define the way that <ProductName>Postgres</ProductName> can functions that you define over a type in turn define the
operate on it. That is, <ProductName>Postgres</ProductName> will only store and way that <ProductName>Postgres</ProductName> can operate
retrieve the data from disk and use your user-defined on it. That is, <ProductName>Postgres</ProductName> will
functions to input, process, and output the data. only store and retrieve the data from disk and use your
user-defined functions to input, process, and output the data.
Base types can have one of three internal formats: Base types can have one of three internal formats:
<ItemizedList> <ItemizedList>
<ListItem><Para>pass by value, fixed-length</Para> <ListItem><Para>pass by value, fixed-length</Para>
@ -254,14 +259,16 @@ The reason why, in general, we must use the function
<Para> <Para>
By-value types can only be 1, 2 or 4 bytes in length By-value types can only be 1, 2 or 4 bytes in length
(even if your computer supports by-value types of other (even if your computer supports by-value types of other
sizes). <ProductName>Postgres</ProductName> itself only passes integer types by sizes). <ProductName>Postgres</ProductName> itself
value. You should be careful to define your types such only passes integer types by value. You should be careful
that they will be the same size (in bytes) on all to define your types such that they will be the same
architectures. For example, the <Acronym>long</Acronym> type is dangerous size (in bytes) on all architectures. For example, the
because it is 4 bytes on some machines and 8 bytes on <Acronym>long</Acronym> type is dangerous because it
others, whereas <Acronym>int</Acronym> type is 4 bytes on most <Acronym>UNIX</Acronym> is 4 bytes on some machines and 8 bytes on others, whereas
machines (though not on most personal computers). A <Acronym>int</Acronym> type is 4 bytes on most
reasonable implementation of the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym> <Acronym>UNIX</Acronym> machines (though not on most
personal computers). A reasonable implementation of
the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym>
machines might be: machines might be:
<ProgramListing> <ProgramListing>
@ -277,9 +284,10 @@ The reason why, in general, we must use the function
<ProgramListing> <ProgramListing>
/* 16-byte structure, passed by reference */ /* 16-byte structure, passed by reference */
typedef struct { typedef struct
char data[16]; {
} char16; double x, y;
} Point;
</ProgramListing> </ProgramListing>
</Para> </Para>
@ -308,10 +316,10 @@ The reason why, in general, we must use the function
<Para> <Para>
Obviously, the data field is not long enough to hold Obviously, the data field is not long enough to hold
all possible strings -- it's impossible to declare such all possible strings -- it's impossible to declare such
a structure in <Acronym>C</Acronym>. When manipulating variable-length a structure in <Acronym>C</Acronym>. When manipulating
types, we must be careful to allocate the correct variable-length types, we must be careful to allocate
amount of memory and initialize the length field. For the correct amount of memory and initialize the length field.
example, if we wanted to store 40 bytes in a text For example, if we wanted to store 40 bytes in a text
structure, we might use a code fragment like this: structure, we might use a code fragment like this:
<ProgramListing> <ProgramListing>
#include "postgres.h" #include "postgres.h"
@ -332,23 +340,30 @@ The reason why, in general, we must use the function
<ProgramListing> <ProgramListing>
#include &lt;string.h&gt; #include &lt;string.h&gt;
#include "postgres.h" #include "postgres.h"
/* By Value */
int int
add_one(int arg) add_one(int arg)
{ {
return(arg + 1); return(arg + 1);
} }
text *
concat_text(text *arg1, text *arg2)
{
int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
memset((void *) new_text, 0, new_text_size); /* By Reference, Fixed Length */
VARSIZE(new_text) = new_text_size;
strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ); Point *
strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ); makepoint(Point *pointx, Point *pointy )
return (new_text); {
Point *new_point = (Point *) palloc(sizeof(Point));
new_point->x = pointx->x;
new_point->y = pointy->y;
return new_point;
} }
/* By Reference, Variable Length */
text * text *
copytext(text *t) copytext(text *t)
{ {
@ -366,6 +381,19 @@ The reason why, in general, we must use the function
VARSIZE(t)-VARHDRSZ); /* how many bytes */ VARSIZE(t)-VARHDRSZ); /* how many bytes */
return(new_t); return(new_t);
} }
text *
concat_text(text *arg1, text *arg2)
{
int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
memset((void *) new_text, 0, new_text_size);
VARSIZE(new_text) = new_text_size;
strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
return (new_text);
}
</ProgramListing> </ProgramListing>
</Para> </Para>
@ -374,13 +402,16 @@ The reason why, in general, we must use the function
<ProgramListing> <ProgramListing>
CREATE FUNCTION add_one(int4) RETURNS int4 CREATE FUNCTION add_one(int4) RETURNS int4
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c'; AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION makepoint(point, point) RETURNS point
AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION concat_text(text, text) RETURNS text CREATE FUNCTION concat_text(text, text) RETURNS text
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c'; AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION copytext(text) RETURNS text CREATE FUNCTION copytext(text) RETURNS text
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c'; AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
</ProgramListing> </ProgramListing>
</Para> </Para>
@ -399,11 +430,11 @@ The reason why, in general, we must use the function
null fields. In addition, composite types that are null fields. In addition, composite types that are
part of an inheritance hierarchy may have different part of an inheritance hierarchy may have different
fields than other members of the same inheritance hierarchy. fields than other members of the same inheritance hierarchy.
Therefore, <ProductName>Postgres</ProductName> provides a procedural Therefore, <ProductName>Postgres</ProductName> provides
interface for accessing fields of composite types from a procedural interface for accessing fields of composite types
C. from C. As <ProductName>Postgres</ProductName> processes
As <ProductName>Postgres</ProductName> processes a set of instances, each instance a set of instances, each instance will be passed into your
will be passed into your function as an opaque structure of type <Acronym>TUPLE</Acronym>. function as an opaque structure of type <Acronym>TUPLE</Acronym>.
Suppose we want to write a function to answer the query Suppose we want to write a function to answer the query
<ProgramListing> <ProgramListing>
* SELECT name, c_overpaid(EMP, 1500) AS overpaid * SELECT name, c_overpaid(EMP, 1500) AS overpaid
@ -414,9 +445,10 @@ The reason why, in general, we must use the function
<ProgramListing> <ProgramListing>
#include "postgres.h" #include "postgres.h"
#include "libpq-fe.h" /* for TUPLE */ #include "executor/executor.h" /* for GetAttributeByName() */
bool bool
c_overpaid(TUPLE t,/* the current instance of EMP */ c_overpaid(TupleTableSlot *t, /* the current instance of EMP */
int4 limit) int4 limit)
{ {
bool isnull = false; bool isnull = false;
@ -430,16 +462,17 @@ The reason why, in general, we must use the function
</Para> </Para>
<Para> <Para>
<Acronym>GetAttributeByName</Acronym> is the <ProductName>Postgres</ProductName> system function that <Acronym>GetAttributeByName</Acronym> is the
<ProductName>Postgres</ProductName> system function that
returns attributes out of the current instance. It has returns attributes out of the current instance. It has
three arguments: the argument of type TUPLE passed into three arguments: the argument of type TUPLE passed into
the function, the name of the desired attribute, and a the function, the name of the desired attribute, and a
return parameter that describes whether the attribute return parameter that describes whether the attribute
is null. <Acronym>GetAttributeByName</Acronym> will align data properly is null. <Acronym>GetAttributeByName</Acronym> will
so you can cast its return value to the desired type. align data properly so you can cast its return value to
For example, if you have an attribute name which is of the desired type. For example, if you have an attribute
the type name, the <Acronym>GetAttributeByName</Acronym> call would look name which is of the type name, the <Acronym>GetAttributeByName</Acronym>
like: call would look like:
<ProgramListing> <ProgramListing>
char *str; char *str;
... ...
@ -448,8 +481,8 @@ The reason why, in general, we must use the function
</Para> </Para>
<Para> <Para>
The following query lets <ProductName>Postgres</ProductName> know about the The following query lets <ProductName>Postgres</ProductName>
c_overpaid function: know about the c_overpaid function:
<ProgramListing> <ProgramListing>
* CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool * CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c'; AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
@ -470,24 +503,28 @@ The reason why, in general, we must use the function
We now turn to the more difficult task of writing We now turn to the more difficult task of writing
programming language functions. Be warned: this section programming language functions. Be warned: this section
of the manual will not make you a programmer. You must of the manual will not make you a programmer. You must
have a good understanding of <Acronym>C</Acronym> (including the use of have a good understanding of <Acronym>C</Acronym>
pointers and the malloc memory manager) before trying (including the use of pointers and the malloc memory manager)
to write <Acronym>C</Acronym> functions for use with <ProductName>Postgres</ProductName>. before trying to write <Acronym>C</Acronym> functions for
While it may be possible to load functions written in use with <ProductName>Postgres</ProductName>. While it may
languages other than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>, this is often be possible to load functions written in languages other
difficult (when it is possible at all) because other than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>,
languages, such as <Acronym>FORTRAN</Acronym> and <Acronym>Pascal</Acronym> often do not follow this is often difficult (when it is possible at all)
the same "calling convention" as <Acronym>C</Acronym>. That is, other because other languages, such as <Acronym>FORTRAN</Acronym>
and <Acronym>Pascal</Acronym> often do not follow the same
"calling convention" as <Acronym>C</Acronym>. That is, other
languages do not pass argument and return values languages do not pass argument and return values
between functions in the same way. For this reason, we between functions in the same way. For this reason, we
will assume that your programming language functions will assume that your programming language functions
are written in <Acronym>C</Acronym>. are written in <Acronym>C</Acronym>.
The basic rules for building <Acronym>C</Acronym> functions are as follows: The basic rules for building <Acronym>C</Acronym> functions
are as follows:
<ItemizedList> <ItemizedList>
<ListItem> <ListItem>
<Para> <Para>
Most of the header (include) files for <ProductName>Postgres</ProductName> Most of the header (include) files for
<ProductName>Postgres</ProductName>
should already be installed in should already be installed in
<FileName>PGROOT/include</FileName> (see Figure 2). <FileName>PGROOT/include</FileName> (see Figure 2).
You should always include You should always include
@ -511,9 +548,11 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
</para> </para>
</ListItem> </ListItem>
<ListItem> <ListItem>
<Para> When allocating memory, use the <ProductName>Postgres</ProductName> <Para> When allocating memory, use the
<ProductName>Postgres</ProductName>
routines palloc and pfree instead of the routines palloc and pfree instead of the
corresponding <Acronym>C</Acronym> library routines malloc and free. corresponding <Acronym>C</Acronym> library routines
malloc and free.
The memory allocated by palloc will be freed The memory allocated by palloc will be freed
automatically at the end of each transaction, automatically at the end of each transaction,
preventing memory leaks. preventing memory leaks.
@ -531,15 +570,16 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
</Para> </Para>
</ListItem> </ListItem>
<ListItem> <ListItem>
<Para> Most of the internal <ProductName>Postgres</ProductName> types are declared <Para> Most of the internal <ProductName>Postgres</ProductName>
in postgres.h, so it's a good idea to always types are declared in postgres.h, so it's a good
include that file as well. Including postgres.h idea to always include that file as well. Including
will also include elog.h and palloc.h for you. postgres.h will also include elog.h and palloc.h for you.
</Para> </Para>
</ListItem> </ListItem>
<ListItem> <ListItem>
<Para> Compiling and loading your object code so that <Para> Compiling and loading your object code so that
it can be dynamically loaded into <ProductName>Postgres</ProductName> it can be dynamically loaded into
<ProductName>Postgres</ProductName>
always requires special flags. See Appendix A always requires special flags. See Appendix A
for a detailed explanation of how to do it for for a detailed explanation of how to do it for
your particular operating system. your particular operating system.