Sql语句查询优化总结:

Sql语句查询优化总结:

Date:2007.1.10

t_supervise_job_assign表如下：

id | building_id

1 | 101

2 | 101

3 | 102

4 | 103

5 | 103

为了取出（select count(*) from t_supervise_job_assign where building_id=a.id）同一building_id不同id的building_id数量，得到如下的表ct：

building_id | total

101 2

102 1

103 2

下面的查询用了子查询，通过building_id=a.id连外层的表，这样的查询效率超低，甚至查死数据库：

select distinct a.id,a.building_name,f.record_person ,d.address,d.begin_date,
(select count(*) from t_supervise_job_assign where building_id=a.id) status,
a.create_user
from t_building a ,
t_building_info d,t_monitor_plan e,t_monitor_record f
where a.id=d.building_id
AND e.f1_id=a.id
AND e.stream_id=f.f1_stream_id
AND a.modify_flag<>'D'
AND a.building_name like '%顺德%' order by status,d.begin_date desc

修改后：

主要优化这条语句：

select count(*) from t_supervise_job_assign where building_id=a.id

优化后：

select t.building_id,count(t.id) as total from t_supervise_job_assign t group by t.building_id

整合为一个表：

再得到最终优化后的查询语句：

select distinct a.id,a.building_name,f.record_person ,d.address,d.begin_date,
ct.status,
a.create_user
from t_building a ,
(select t.building_id,count(t.id) as status from t_supervise_job_assign t group by t.building_id) ct,
t_building_info d,t_monitor_plan e,t_monitor_record f
where a.id=d.building_id
AND e.f1_id=a.id
AND ct.building_id(+)=a.id
AND e.stream_id=f.f1_stream_id
AND a.modify_flag<>'D'
AND a.building_name like '%顺德%' order by status,d.begin_date desc