On Tue, Apr 26, 2005 at 01:58:09PM -0400, Ying Lu wrote: > > A question about index. It mentioned in postgresql 8.0 doc "a query or > data manipulation command can use *at most one index* *per table*". An > example query is: > > select * from A left join B using (id) where A.type='apple' and > A.isExport=true; > > "id" is the primary key for both table A & B. If index (type, isExport) > has been created for table A. In the above query, will this index works? You can use EXPLAIN to see the query plan, including which indexes will be used. See "Using EXPLAIN" in the "Performance Tips" chapter of the documentation. http://www.postgresql.org/docs/8.0/interactive/performance-tips.html#USING-EXPLAIN http://www.postgresql.org/docs/8.0/interactive/sql-explain.html A query won't necessarily use an index if one is available: if the planner thinks a sequential scan will be faster than using an index, then it won't use the index. If you want to see whether an index scan *could* be used, then set enable_seqscan to off before running EXPLAIN. -- Michael Fuhr http://www.fuhr.org/~mfuhr/ ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to majordomo@xxxxxxxxxxxxxx
