Tobe honest,I've alreadystartedwritingcodetodothis,butI'm facedwitha
misunderstandingof howto correctlycreatea
conditionfor"OR"expressionsthatare notsubjectto transformation.
For example,the expressions b=1in the query below:
alena@postgres=# explain select * from x where ( (a =5 or a=4) and a =
ANY(ARRAY[5,4])) or (b=1); QUERY PLAN
----------------------------------------------------------------------------------
Seq Scan on x (cost=0.00..123.00 rows=1 width=8) Filter: ((((a = 5) OR
(a = 4)) AND (a = ANY ('{5,4}'::integer[]))) OR (b = 1)) (2 rows)
I see that two expressions have remained unchanged and it only works
for "AND" binary operations.
But I think it might be worth applying this together, where does the
optimizer generate indexes (build_paths_for_OR function)?
Sorry, it works) I needed to create one more index for b column.
Just in case, I gave an example of a complete case, otherwise it might
not be entirely clear:
alena@postgres=# create table x (a int, b int);
CREATE TABLE
alena@postgres=# create index a_idx on x(a);
insert into x select id,id from
generate_series(1, 5000) as id;
CREATE INDEX
INSERT 0 5000
alena@postgres=# analyze;
ANALYZE
alena@postgres=# explain select * from x where ( (a =5 or a=4) and a =
ANY(ARRAY[5,4])) or (b=1); QUERY PLAN
----------------------------------------------------------------------------------
Seq Scan on x (cost=0.00..123.00 rows=1 width=8) Filter: ((((a = 5) OR
(a = 4)) AND (a = ANY ('{5,4}'::integer[]))) OR (b = 1)) (2 rows)
alena@postgres=# create index b_idx on x(b);
CREATE INDEX
alena@postgres=# explain select * from x where ( (a =5 or a=4) and a =
ANY(ARRAY[5,4])) or (b=1);
QUERY PLAN
--------------------------------------------------------------------------
Bitmap Heap Scan on x (cost=12.87..21.68 rows=1 width=8)
Recheck Cond: ((a = ANY ('{5,4}'::integer[])) OR (b = 1))
-> BitmapOr (cost=12.87..12.87 rows=3 width=0)
-> Bitmap Index Scan on a_idx (cost=0.00..8.58 rows=2 width=0)
Index Cond: (a = ANY ('{5,4}'::integer[]))
-> Bitmap Index Scan on b_idx (cost=0.00..4.29 rows=1 width=0)
Index Cond: (b = 1)
(7 rows)
--
Regards,
Alena Rybakina
Postgres Professional:http://www.postgrespro.com
The Russian Postgres Company
