多表联合查询

tb_Project表：

ID	ProjectCreater	ProjectPrincipal	...
1	1	2	...

tb_User表：

ID	UserRealName
1	张三
2	李四

select a.*,b.UserRealName as Creater,c.UserRealName as Principal 
from tb_Project a, tb_User b, tb_User c 
where 
a.ProjectCreater=b.ID and a.ProjectPrincipal=c.ID

 结果： 

tb_Project表：

ID	ProjectCreater	ProjectPrincipal	...	Creater	Principal
1	1	2	...	张三	李四