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 |
