我有一个查询,比如: (case when exists(select 1 from t_approved_phonenumber where phone_number = m.c_phone_number) then 1 else 0 end) as approved,
(case when exists(select 1 from t_log log where log.c_id < m.m_log_id a
下面的代码执行得非常慢,需要很长时间才能执行。即使有一个空的结果集,它大约需要280秒。查询中有几个case语句。一些帮助优化查询将受到高度赞赏。SQL查询:
SELECT @n:=@n+1 No, a.name customer_name, a.id_number AS customer_id, a.email AS email_address