Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Mon May 26 15:25:04 EDT 2003
+ Last updated: Wed May 28 00:35:16 EDT 2003
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
Operational Questions
4.1) What is the difference between binary cursors and normal cursors?
- 4.2) How do I SELECT only the first few rows of a query?
+ 4.2) How do I SELECT only the first few rows of a query? A random row?
4.3) How do I get a list of tables or other things I can see in psql?
4.4) How do you remove a column from a table, or change it's data
type?
See the DECLARE manual page for a description.
- 4.2) How do I SELECT only the first few rows of a query?
+ 4.2) How do I SELECT only the first few rows of a query? A random row?
See the FETCH manual page, or use SELECT ... LIMIT....
evaluate only the first few records requested, or the entire query may
have to be evaluated until the desired rows have been generated.
+ To SELECT a random row, use:
+ SELECT col
+ FROM tab
+ ORDER BY random()
+ LIMIT 1;
+
4.3) How do I get a list of tables or other things I can see in psql?
You can read the source code for psql in file
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Mon May 26 15:25:04 EDT 2003</P>
+ <P>Last updated: Wed May 28 00:35:16 EDT 2003</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
<A href="#4.1">4.1</A>) What is the difference between binary
cursors and normal cursors?<BR>
<A href="#4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the
- first few rows of a query?<BR>
+ first few rows of a query? A random row?<BR>
<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
description.</P>
<H4><A name="4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the
- first few rows of a query?</H4>
+ first few rows of a query? A random row?</H4>
<P>See the <SMALL>FETCH</SMALL> manual page, or use
<SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P>
records requested, or the entire query may have to be evaluated
until the desired rows have been generated.</P>
+ <P>To <SMALL>SELECT</SMALL> a random row, use:
+<PRE>
+ SELECT col
+ FROM tab
+ ORDER BY random()
+ LIMIT 1;
+</PRE>
+
<H4><A name="4.3">4.3</A>) How do I get a list of tables or other
things I can see in <I>psql</I>?</H4>