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Add info about selecting a random row.

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Bruce Momjian 2003-05-28 04:35:28 +00:00
parent a6f01d1aa6
commit a2b498c291
2 changed files with 20 additions and 6 deletions
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doc/FAQ
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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)
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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?
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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....
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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

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doc/src/FAQ/FAQ.html
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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>
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<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
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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>
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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>