从Chat表中，如果UserType是父母，根据UserId 从Parent表中取出Name，

如果是老师,根据UserId 从Teacher表中取出Name，这个查询语句怎么写啊

Chat表

Parent表

Teacher表

http://blog.csdn.net/hurryjiang/article/details/7716395

嵌套sql语句：select name from Teacher where userId=(selsece userId from chat where userType = '老师')

使用case语句查询http://blog.itpub.net/26451903/viewspace-733526

select UserType, case UserType when '老师' then b.Name when '家长' then c.Name end as Name
from Chat a,Teacher b,Parent c
where a.userId=b.userId or a.userId=c.userId