database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-30 21:42:05 +03:00
Code Activity

Update sequence FAQ items, per suggestion from Pavel Stehule.

Browse Source
This commit is contained in:
Bruce Momjian
2007-10-09 19:55:36 +00:00
parent 81f285da7c
commit cd2cf74584
2 changed files with 26 additions and 45 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
doc/src/FAQ/FAQ.html
View File

@ -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
&lt;<I>table</I>&gt;_&lt;<I>serialcolumn</I>&gt;_<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>
<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>
<PRE>
new_id = execute("SELECT nextval('person_id_seq')");
execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
</PRE>
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 &lt;<I>table</I>&gt;_&lt;<I>
serialcolumn</I>&gt;_<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>