MYSQL语句

MYSQL语句 注意写法

3个表都非常大时，原因待查

1.超级耗时（几分钟）

select * from ywlr

left join sys_user suser on suser.dept_id=ywlr.studentid and suser.user_type in(6,8)

left join xxpt_student st on ywlr.studentid=st.id 

where st.school_id=1234 

2.很快（几毫秒）

select * from ywlr

left join sys_user suser on suser.dept_id=ywlr.studentid 

left join xxpt_student st on ywlr.studentid=st.id 

where st.school_id=1234 and suser.user_type in(6,8)