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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 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) Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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Operational Questions Operational Questions
4.1) What is the difference between binary cursors and normal cursors? 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? 4.3) 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 4.4) How do you remove a column from a table, or change it's data
type? type?
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See the DECLARE manual page for a description. 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.... 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 evaluate only the first few records requested, or the entire query may
have to be evaluated until the desired rows have been generated. 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? 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 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"> alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> <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= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> "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 <A href="#4.1">4.1</A>) What is the difference between binary
cursors and normal cursors?<BR> cursors and normal cursors?<BR>
<A href="#4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the <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 <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> things I can see in <I>psql</I>?<BR>
<A href="#4.4">4.4</A>) How do you remove a column from a <A href="#4.4">4.4</A>) How do you remove a column from a
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description.</P> description.</P>
<H4><A name="4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the <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 <P>See the <SMALL>FETCH</SMALL> manual page, or use
<SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P> <SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P>
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records requested, or the entire query may have to be evaluated records requested, or the entire query may have to be evaluated
until the desired rows have been generated.</P> 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 <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> things I can see in <I>psql</I>?</H4>