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| author | Bruce Momjian <bruce@momjian.us> | 2003-10-29 20:20:12 +0000 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2003-10-29 20:20:12 +0000 |
| commit | a00d6b23ebc27d66a090554e2e8c95fb0c26b9e6 (patch) | |
| tree | 23f17a15715396a34fd1825586a3bf0637f2669f /doc/src | |
| parent | a35deb54006523e62f79c72238c62f14ee311940 (diff) | |
| download | postgresql-a00d6b23ebc27d66a090554e2e8c95fb0c26b9e6.tar.gz postgresql-a00d6b23ebc27d66a090554e2e8c95fb0c26b9e6.zip | |
Update for 7.4 --- prefer IN to EXISTS.
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/FAQ/FAQ.html | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 30c03d468c1..b01bbef36ed 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: Fri Oct 10 17:27:02 EDT 2003</P> + <P>Last updated: Wed Oct 29 15:19:43 EST 2003</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> @@ -1303,10 +1303,10 @@ BYTEA bytea variable-length byte array (null-byte safe) <H4><A name="4.22">4.22</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?</H4> - <P>Currently, we join subqueries 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 + <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 * @@ -1320,7 +1320,9 @@ BYTEA bytea variable-length byte array (null-byte safe) </PRE> For this to be fast, <CODE>subcol</CODE> should be an indexed column. - This preformance problem will be fixed in 7.4. + <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="4.23">4.23</A>) How do I perform an outer join?</H4> |