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Add item for changing a column's data type.

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This commit is contained in:
Bruce Momjian
2003-05-26 19:25:20 +00:00
parent 6923ea2b86
commit 90903069e9
2 changed files with 31 additions and 9 deletions
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doc/src/FAQ/FAQ.html
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@ -10,7 +10,7 @@
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Tue Apr 22 14:02:41 EDT 2003</P>
<P>Last updated: Mon May 26 15:25:04 EDT 2003</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@ -87,7 +87,7 @@
<A href="#4.3">4.3</A>) How do I get a list of tables or other
things I can see in <I>psql</I>?<BR>
<A href="#4.4">4.4</A>) How do you remove a column from a
table?<BR>
table, or change it's data type?<BR>
<A href="#4.5">4.5</A>) What is the maximum size for a row, a
table, and a database?<BR>
<A href="#4.6">4.6</A>) How much database disk space is required
@ -822,9 +822,9 @@
execute the commands you give.</P>
<H4><A name="4.4">4.4</A>) How do you remove a column from a
table?</H4>
table, or change its data type?</H4>
<P>This functionality was added in release 7.3 with
<P><SMALL>DROP COLUMN</SMALL> functionality was added in release 7.3 with
<SMALL>ALTER TABLE DROP COLUMN</SMALL>. In earlier versions,
you can do this:</P>
<PRE>
@ -838,6 +838,17 @@
COMMIT;
</PRE>
<P>To change the data type of a column, do this:</P>
<PRE>
BEGIN;
ALTER TABLE tab ADD COLUMN new_col <i>new_data_type</i>;
UPDATE tab SET new_col = CAST(old_col AS <i>new_data_type</i>);
ALTER TABLE DROP COLUMN old_col;
COMMIT;
</PRE>
<P>You might then want to do <I>VACUUM FULL tab</I> to reclaim the
disk space used by the expired rows.</P>
<H4><A name="4.5">4.5</A>) What is the maximum size for a row, a
table, and a database?</H4>