我在嵌套的JSONB字段上创建了一个索引:
CREATE INDEX foo_idx ON some_table(cast(content->'meta'->>'version' AS int));
,但是select查询仍然会进行全表扫描:
select *
from some_table
where (content->'meta'->>'version')::INT <= 9000
LIMIT 1;
我还尝试将查询表达为:
select *
from some_table
where cast(content->'meta'->>'version' AS INT) <= 9000
LIMIT 1;
具有相同的结果。
查询计划:
Limit (cost=0.00..1.06 rows=10 width=52)
-> Seq Scan on some_table (cost=0.00..38429.27 rows=361441 width=52)
Filter: ((((content -> 'meta'::text) ->> 'version'::text))::integer <= 9000)
我在这里想念什么?
编辑:这更是巧合。我在查询中添加了ORDER BY random()
,并获得了以下查询计划:
Limit (cost=31644.83..31644.83 rows=1 width=52) (actual time=0.017..0.017 rows=0 loops=1)
-> Sort (cost=31644.83..32548.43 rows=361441 width=52) (actual time=0.016..0.016 rows=0 loops=1)
Sort Key: (random())
Sort Method: quicksort Memory: 25kB
-> Bitmap Heap Scan on game_object_user (cost=6769.60..29837.62 rows=361441 width=52) (actual time=0.011..0.011 rows=0 loops=1)
Recheck Cond: ((((content -> 'meta'::text) ->> 'version'::text))::integer < 9000)
-> Bitmap Index Scan on foo_idx (cost=0.00..6679.23 rows=361441 width=0) (actual time=0.009..0.009 rows=0 loops=1)
Index Cond: ((((content -> 'meta'::text) ->> 'version'::text))::integer < 90000)
Planning time: 0.074 ms
Execution time: 0.040 ms
使用了索引。