多表之间实现左连接

CPM_TASK_RES表有三个外键,对应CPM_RES_SORT,CPM_RES_TYPE ,CPM_RES 这三个表的主键,想像两个表左连接那样实现四个表的做连接:

方法如下:

 select a.Task_Code, a.Project_Code, a.Res_Num, a.ResSort_Code, b.ResSort_Name,
      a.ResType_Code, c.ResType_Name, a.Res_Code, d .Res_Name

from CPM_TASK_RES as a left join CPM_RES_SORT as b on a.ResSort_Code=b.ResSort_Code left join CPM_RES_TYPE as c on a.ResType_Code=c.ResType_Code left join CPM_RES as d on a.Res_Code=d.Res_Code

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