我有一个名为account_id的整数列的表.我有一个关于该列的索引.
但似乎Postgres不想使用我的索引：
EXPLAIN ANALYZE SELECT "invoices".* FROM "invoices" WHERE "invoices"."account_id" = 1; Seq Scan on invoices (cost=0.00..6504.61 rows=117654 width=186) (actual time=0.021..33.943 rows=118027 loops=1) Filter: (account_id = 1) Rows Removed by Filter: 51462 Total runtime: 39.917 ms (4 rows)
知道为什么会这样吗？
解决方法
因为：
Seq Scan on invoices (...) (actual ... rows=118027 <— this Filter: (account_id = 1) Rows Removed by Filter: 51462 <— vs this Total runtime: 39.917 ms
你选择了这么多行,读取整个表会更便宜.
相关的早期问题和答案从今天开始进一步阅读：
> Why doesn’t Postgresql use index for IN query?
> Postgres using wrong index when querying a view of indexed expressions?
(另请参阅Craig关于第二个问题的更长答案,以获取有关索引细微差别的其他说明.)
