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Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/FAQ/FAQ.html | 23 |
1 files changed, 17 insertions, 6 deletions
diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index ca960bb888f..2a259db3d05 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff"> <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> - <P>Last updated: Tue Dec 5 18:13:32 EST 2006</P> + <P>Last updated: Mon Dec 11 17:44:33 EST 2006</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:bruce@momjian.us">bruce@momjian.us</A>) @@ -86,8 +86,8 @@ searches and case-insensitive regular expression searches? How do I use an index for case-insensitive searches?<BR> <A href="#item4.9">4.9</A>) In a query, how do I detect if a field - is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL> - NULL</SMALL> or not?<BR> + is <SMALL>NULL</SMALL>? How do I concatenate possible <SMALL>NULL</SMALL>s? + How can I sort on whether a field is <SMALL> NULL</SMALL> or not?<BR> <A href="#item4.10">4.10</A>) What is the difference between the various character types?<BR> <A href="#item4.11.1">4.11.1</A>) How do I create a @@ -823,10 +823,14 @@ table?</TD><TD>unlimited</TD></TR> identical values that differ only in case. To force a particular case to be stored in the column, use a <SMALL>CHECK</SMALL> constraint or a trigger.</P> - + + <A href="#item4.9">4.9</A>) In a query, how do I detect if a field + is <SMALL>NULL</SMALL>? How do I concatenate possible <SMALL>NULL</SMALL>s? + How can I sort on whether a field is <SMALL> NULL</SMALL> or not?<BR> + <H3 id="item4.9">4.9) In a query, how do I detect if a field - is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL> - NULL</SMALL> or not?</H3> + is <SMALL>NULL</SMALL>? How do I concatenate possible <SMALL>NULL</SMALL>s? + How can I sort on whether a field is <SMALL> NULL</SMALL> or not?</H3> <P>You test the column with <SMALL>IS NULL</SMALL> and <SMALL>IS NOT NULL</SMALL>, like this:</P> @@ -837,6 +841,13 @@ table?</TD><TD>unlimited</TD></TR> WHERE col IS NULL; </PRE> + <P>To concatentate with possible <SMALL>NULL</SMALL>s, use <I>COALESCE()</I>, + like this:</P> +<PRE> + SELECT COALESCE(col1, '') || COALESCE(col2, '') + FROM tab +</PRE> + <P>To sort by the <SMALL>NULL</SMALL> status, use the <SMALL>IS NULL</SMALL> and <SMALL>IS NOT NULL</SMALL> modifiers in your <SMALL>ORDER BY</SMALL> clause. Things that are <I>true</I> will sort higher than things that are <I>false</I>, |