表结构:
id和userID为单索引
以下查询用时2.36秒
SELECT ull.* FROM userLoginLog ull WHERE NOT EXISTS
(
SELECT 1 FROM userLoginLog
WHERE 1=1
AND ull.userId = userId
AND id > ull.id
)
以下查询用时0.1秒
SELECT ull.* FROM userLoginLog ull WHERE NOT EXISTS
(
SELECT 1 FROM userLoginLog
WHERE 1=1
AND ull.userId = userId
AND id < ull.id
)
为什么差距这么大?