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Diffstat (limited to 'doc/FAQ')
| -rw-r--r-- | doc/FAQ | 28 |
1 files changed, 23 insertions, 5 deletions
@@ -96,6 +96,7 @@ 4.21) My large-object operations get invalid large obj descriptor. Why? 4.22) How do I create a column that will default to the current time? + 4.23) Why are my subqueries using IN so slow? Extending PostgreSQL @@ -198,8 +199,8 @@ Unix/NT porting library. See pgsql/doc/README.NT in the distribution. There is also a web page at - http://members.tripod.com/~kevlo/postgres/portNT.html. There is - another port using U/Win at http://surya.wipro.com/uwin/ported.html. + http://www.freebsd.org/~kevlo/postgres/portNT.html. There is another + port using U/Win at http://surya.wipro.com/uwin/ported.html. 1.5) Where can I get PostgreSQL? @@ -913,10 +914,27 @@ BYTEA bytea variable-length array of bytes but this makes the column default to the time of table creation, not the time of row insertion. Instead do: - create table test (x int, modtime timestamp default text 'now'); + CREATE TABLE test (x int, modtime timestamp default now() ); - The casting of the value to text prevents the default value from being - computed at table creation time, and delays it until insertion time. + The calling of the function now() prevents the default value from + being computed at table creation time, and delays it until insertion + time. We believe this will not be a problem in post-6.5.* releases. + + 4.23) Why are my subqueries using IN so slow? + + Currently, we join subqueries to outer queries by sequential scanning + the result of the subquery for each row of the outer query. A + workaround is to replace IN with EXISTS. For example, change: + SELECT * + FROM tab + WHERE col1 IN (SELECT col2 FROM TAB2) + + to: + SELECT * + FROM tab + WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2) + + We hope to fix this limitation in a future release. _________________________________________________________________ Extending PostgreSQL |