索引跨越PostgreSQL中的多个表

Question

Is it possible in PostgreSQL to place an index on an expression containing fields of multiple tables. So for example an index to speed up an query of the following form:

SELECT *, (table1.x + table2.x) AS z
FROM table1
INNER JOIN table2
ON table1.id = table2.id
ORDER BY z ASC

Answer 1

No it's not possible to have an index on many tables, also it really wouldn't guarantee speeding up anything since you won't always get an Index Only Scan. What you really want is a materialized view but pg doesn't have those either. You can try implementing it yourself using triggers like this or this .

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Update

As noted by @petter. The materialized views were introduced in 9.3 .

Answer 2

No, that's not possible in any currently shipping SQL dbms. Oracle supports bitmap join indexes , but that might not be relevant. It's not clear to me whether you want an index on only the join columns of multiple tables, or whether you want an index on arbitrary columns of joined tables.

To determine the real source of performance problems, learn to read the output of PostgreSQL's EXPLAIN ANALYZE .