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Diffstat (limited to 'doc/src/FAQ/FAQ.html')
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1 files changed, 11 insertions, 37 deletions
diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 0b8401ec2ac..d79d62c06e4 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: Sat Jan 29 23:15:42 EST 2005</P> + <P>Last updated: Sat Jan 29 23:20:03 EST 2005</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> @@ -114,16 +114,14 @@ <I>"invalid large obj descriptor"</I>?<BR> <A href="#4.17">4.17</A>) How do I create a column that will default to the current time?<BR> - <A href="#4.18">4.18</A>) Why are my subqueries using - <CODE><SMALL>IN</SMALL></CODE> so slow?<BR> - <A href="#4.19">4.19</A>) How do I perform an outer join?<BR> - <A href="#4.20">4.20</A>) How do I perform queries using multiple + <A href="#4.18">4.18</A>) How do I perform an outer join?<BR> + <A href="#4.19">4.19</A>) How do I perform queries using multiple databases?<BR> - <A href="#4.21">4.21</A>) How do I return multiple rows or columns + <A href="#4.20">4.20</A>) How do I return multiple rows or columns from a function?<BR> - <A href="#4.22">4.22</A>) Why can't I reliably create/drop + <A href="#4.21">4.21</A>) Why can't I reliably create/drop temporary tables in PL/PgSQL functions?<BR> - <A href="#4.23">4.23</A>) What encryption options are available?<BR> + <A href="#4.22">4.22</A>) What encryption options are available?<BR> <H2 align="center">Extending PostgreSQL</H2> @@ -1155,31 +1153,7 @@ BYTEA bytea variable-length byte array (null-byte safe) </CODE> </PRE> - <H4><A name="4.18">4.18</A>) Why are my subqueries using - <CODE><SMALL>IN</SMALL></CODE> so slow?</H4> - - <P>In versions prior to 7.4, subqueries were joined to outer queries - by sequentially scanning the result of the subquery for each row of - the outer query. If the subquery returns only a few rows and the outer - query returns many rows, <CODE><SMALL>IN</SMALL></CODE> is fastest. To - speed up other queries, replace <CODE>IN</CODE> with - <CODE>EXISTS</CODE>:</P> -<PRE> SELECT * - FROM tab - WHERE col IN (SELECT subcol FROM subtab); -</PRE> - to: -<PRE> SELECT * - FROM tab - WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col); -</PRE> - - For this to be fast, <CODE>subcol</CODE> should be an indexed column. - <P>In version 7.4 and later, <CODE>IN</CODE> actually uses the same - sophisticated join techniques as normal queries, and is prefered - to using <CODE>EXISTS</CODE>. - - <H4><A name="4.19">4.19</A>) How do I perform an outer join?</H4> + <H4><A name="4.18">4.18</A>) How do I perform an outer join?</H4> <P>PostgreSQL supports outer joins using the SQL standard syntax. Here are two examples:</P> @@ -1219,7 +1193,7 @@ BYTEA bytea variable-length byte array (null-byte safe) ORDER BY col1 </PRE> - <H4><A name="4.20">4.20</A>) How do I perform queries using + <H4><A name="4.19">4.19</A>) How do I perform queries using multiple databases?</H4> <P>There is no way to query a database other than the current one. @@ -1231,7 +1205,7 @@ BYTEA bytea variable-length byte array (null-byte safe) connections to different databases and merge the results on the client side.</P> - <H4><A name="4.21">4.21</A>) How do I return multiple rows or + <H4><A name="4.20">4.20</A>) How do I return multiple rows or columns from a function?</H4> <P>In 7.3, you can easily return multiple rows or columns from a @@ -1239,7 +1213,7 @@ BYTEA bytea variable-length byte array (null-byte safe) <a href="http://techdocs.postgresql.org/guides/SetReturningFunctions"> http://techdocs.postgresql.org/guides/SetReturningFunctions</a>. - <H4><A name="4.22">4.22</A>) Why can't I reliably create/drop + <H4><A name="4.21">4.21</A>) Why can't I reliably create/drop temporary tables in PL/PgSQL functions?</H4> <P>PL/PgSQL caches function contents, and an unfortunate side effect is that if a PL/PgSQL function accesses a temporary table, and that @@ -1249,7 +1223,7 @@ BYTEA bytea variable-length byte array (null-byte safe) <SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This will cause the query to be reparsed every time.</P> - <H4><A name="4.23">4.23</A>) What encryption options are available? + <H4><A name="4.22">4.22</A>) What encryption options are available? </H4> <UL> <LI><I>contrib/pgcrypto</I> contains many encryption functions for |