From cd2cf74584b3938cb79dae83a87bf52d0e6ee75f Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Tue, 9 Oct 2007 19:55:36 +0000 Subject: [PATCH] Update sequence FAQ items, per suggestion from Pavel Stehule. --- doc/FAQ | 29 ++++++++++------------------- doc/src/FAQ/FAQ.html | 42 ++++++++++++++++-------------------------- 2 files changed, 26 insertions(+), 45 deletions(-) diff --git a/doc/FAQ b/doc/FAQ index 9b06e5ac5c..f35ada2c58 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Mon Oct 8 23:19:46 EDT 2007 + Last updated: Tue Oct 9 15:52:10 EDT 2007 Current maintainer: Bruce Momjian (bruce@momjian.us) @@ -697,29 +697,20 @@ name TEXT ); - See the create_sequence manual page for more information about - sequences. + Automatically created sequence are named __seq, + where table and serialcolumn are the names of the table and SERIAL + column, respectively. See the create_sequence manual page for more + information about sequences. 4.11.2) How do I get the value of a SERIAL insert? - One approach is to retrieve the next SERIAL value from the sequence - object with the nextval() function before inserting and then insert it - explicitly. Using the example table in 4.11.1, an example in a - pseudo-language would look like this: - new_id = execute("SELECT nextval('person_id_seq')"); - execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')"); + The simplest way is to retrieve the assigned SERIAL value with + RETURNING. Using the example table in 4.11.1, it would look like this: + INSERT INTO person (name) VALUES ('Blaise Pascal') RETURNING id; - 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 - the name of the automatically created SEQUENCE object will be named -
_< serialcolumn>_seq, where table and serialcolumn are the - names of your table and your SERIAL column, respectively. + You can also call nextval() and use that value in the INSERT, or call + currval() after the INSERT. - Alternatively, you could retrieve the assigned SERIAL value with the - currval() function after it was inserted by default, e.g., - execute("INSERT INTO person (name) VALUES ('Blaise Pascal')"); - new_id = execute("SELECT currval('person_id_seq')"); - 4.11.3) Doesn't currval() lead to a race condition with other users? No. currval() returns the current value assigned by your session, not diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 410c2c6f55..3a3235eaa6 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff">

Frequently Asked Questions (FAQ) for PostgreSQL

-

Last updated: Mon Oct 8 23:19:46 EDT 2007

+

Last updated: Tue Oct 9 15:52:10 EDT 2007

Current maintainer: Bruce Momjian (bruce@momjian.us) @@ -916,38 +916,28 @@ length ); - See the create_sequence manual page for more information - about sequences. +

Automatically created sequence are named + <table>_<serialcolumn>_seq, where + table and serialcolumn are the names of the table and + SERIAL column, respectively. See the + create_sequence manual page for more information about + sequences.

4.11.2) How do I get the value of a SERIAL insert?

-

One approach is to retrieve the next SERIAL value - from the sequence object with the nextval() function - before inserting and then insert it explicitly. Using the - example table in 4.11.1, an example in a - pseudo-language would look like this:

+

The simplest way is to retrieve the assigned SERIAL + value with RETURNING. Using the example table in 4.11.1, it would look like this:

+ 
-    new_id = execute("SELECT nextval('person_id_seq')");
-    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 other queries (e.g., as a foreign key to the person - table). Note that the name of the automatically created - SEQUENCE object will be named <table>_< - serialcolumn>_seq, where table and serialcolumn - are the names of your table and your SERIAL column, - respectively. - -

Alternatively, you could retrieve the assigned SERIAL - value with the currval() function after it was inserted by - default, e.g.,

-
-    execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
-    new_id = execute("SELECT currval('person_id_seq')");
+    INSERT INTO person (name) VALUES ('Blaise Pascal') RETURNING id;
+ You can also call nextval() and use that value in the + INSERT, or call currval()after the + INSERT. +

4.11.3) Doesn't currval() lead to a race condition with other users?