diff --git a/doc/FAQ b/doc/FAQ index a98ec31123..bec9455b98 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Fri Oct 10 17:27:02 EDT 2003 + Last updated: Wed Oct 29 15:19:43 EST 2003 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) @@ -1031,11 +1031,11 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP ); 4.22) Why are my subqueries using IN so slow? - 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, IN is fastest. To speed up other queries, replace IN with - EXISTS: + 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, IN is fastest. To speed up other queries, + replace IN with EXISTS: SELECT * FROM tab WHERE col IN (SELECT subcol FROM subtab); @@ -1045,8 +1045,10 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP ); FROM tab WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col); - For this to be fast, subcol should be an indexed column. This - preformance problem will be fixed in 7.4. + For this to be fast, subcol should be an indexed column. + + In version 7.4 and later, IN actually uses the same sophisticated join + techniques as normal queries, and is prefered to using EXISTS. 4.23) How do I perform an outer join? diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 30c03d468c..b01bbef36e 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff">
Last updated: Fri Oct 10 17:27:02 EDT 2003
+Last updated: Wed Oct 29 15:19:43 EST 2003
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@@ -1303,10 +1303,10 @@ BYTEA bytea variable-length byte array (null-byte safe)
IN
so slow?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, IN
is fastest. To
+
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, IN
is fastest. To
speed up other queries, replace IN
with
EXISTS
:
SELECT * @@ -1320,7 +1320,9 @@ BYTEA bytea variable-length byte array (null-byte safe)For this to be fast,
subcol
should be an indexed column.
- This preformance problem will be fixed in 7.4.
+ In version 7.4 and later, IN
actually uses the same
+ sophisticated join techniques as normal queries, and is prefered
+ to using EXISTS
.