Sql 左完全链接

 

--用虚表加过滤条件后在连接，保证左表数据记录数不减少

SELECT  a.PID, a.MID, a.SN, a.Name, a.Model, a.BrandName, a.Unit, b.Name AS UnitName, a.TaxRate, a.CanUse, a.Remark
FROM    dbo.tbMaterialList AS a LEFT OUTER JOIN
             (SELECT   PID, Name   FROM   dbo.tbDictDataTree   WHERE     (MID = 5)) AS b 
ON a.Unit = b.PID

 

SELECT a.PID, a.FID, a.SN, a.Name, b.FlowID
 FROM  dbo.tbWorkFlowState AS a LEFT OUTER JOIN
 (SELECT FlowID FROM   dbo.tbUserFlow  WHERE (UserID = 1)) AS b ON a.PID = b.FlowID
   WHERE (a.StateValue > 1) AND (a.FID = 13)