From cd2cf74584b3938cb79dae83a87bf52d0e6ee75f Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Tue, 9 Oct 2007 19:55:36 +0000
Subject: [PATCH] Update sequence FAQ items, per suggestion from Pavel Stehule.
---
doc/FAQ | 31 +++++++++++--------------------
doc/src/FAQ/FAQ.html | 40 +++++++++++++++-------------------------
2 files changed, 26 insertions(+), 45 deletions(-)
diff --git a/doc/FAQ b/doc/FAQ
index 9b06e5ac5c9..f35ada2c58b 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 <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:
- 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')");
+ 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 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?
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 410c2c6f551..3a3235eaa6b 100644
--- a/doc/src/FAQ/FAQ.html
+++ b/doc/src/FAQ/FAQ.html
@@ -10,7 +10,7 @@
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Mon Oct 8 23:19:46 EDT 2007</P>
+ <P>Last updated: Tue Oct 9 15:52:10 EDT 2007</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:bruce@momjian.us">bruce@momjian.us</A>)
@@ -916,38 +916,28 @@ length</TD></TR>
);
</PRE>
- See the <I>create_sequence</I> manual page for more information
- about sequences.
+ <P>Automatically created sequence are named
+ <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where
+ <I>table</I> and <I>serialcolumn</I> are the names of the table and
+ <SMALL>SERIAL</SMALL> column, respectively. See the
+ <I>create_sequence</I> manual page for more information about
+ sequences.</P>
<H3 id="item4.11.2">4.11.2) How do I get the value of a
<SMALL>SERIAL</SMALL> insert?</H3>
- <P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value
- from the sequence object with the <I>nextval()</I> function
- <I>before</I> inserting and then insert it explicitly. Using the
- example table in <A href="#item4.11.1">4.11.1</A>, an example in a
- pseudo-language would look like this:</P>
-<PRE>
- new_id = execute("SELECT nextval('person_id_seq')");
- execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
-</PRE>
+ <P>The simplest way is to retrieve the assigned <SMALL>SERIAL</SMALL>
+ value with <SMALL>RETURNING</SMALL>. Using the example table in <A
+ href="#item4.11.1">4.11.1</A>, it would look like this:</P>
- You would then also have the new value stored in <CODE>new_id</CODE>
- for use in other queries (e.g., as a foreign key to the <CODE>person
- </CODE> table). Note that the name of the automatically created
- <SMALL>SEQUENCE</SMALL> object will be named <<I>table</I>>_<<I>
- serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I>
- are the names of your table and your <SMALL>SERIAL</SMALL> column,
- respectively.
-
- <P>Alternatively, you could retrieve the assigned <SMALL>SERIAL</SMALL>
- value with the <I>currval()</I> function <I>after</I> it was inserted by
- default, e.g.,</P>
<PRE>
- 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;
</PRE>
+ You can also call <I>nextval()</I> and use that value in the
+ <SMALL>INSERT</SMALL>, or call <I>currval()</I> <I>after</I> the
+ <SMALL>INSERT</SMALL>.
+
<H3 id="item4.11.3">4.11.3) Doesn't <I>currval()</I>
lead to a race condition with other users?</H3>
--
GitLab