[转]sql 左右连接 on 条件注意事项

select * FROM View_VehicleContractInfo vci WITH(NOLOCK)
LEFT JOIN AuctionVehicle av WITH(NOLOCK)
ON vci.VehicleContractID = av.VehicleContractID
AND av.AuctionID = (SELECT MAX(AuctionVehicle.AuctionID) FROM AuctionVehicle WHERE AuctionVehicle.VehicleContractID IN ('+@VehicleCode+'))
LEFT JOIN View_VehicleServiceInfo AS VS
ON vci.VehicleCode = VS.VehicleCode
AND VS.ServiceCustomerTypeCode=''S''
AND VS.ServiceSettlePrice<>0 and VS.auctionid=av.auctionid
LEFT JOIN StoreManagement AS SM ON vci.VehicleCode = SM.GPcode
WHERE vci.VehicleContractID IN ('+@VehicleCode+')

例如上面的代码 在左右连接的时候如果没有值则用null代替，这就使得on下和连接无关的条件失效

如 1. AND VS.ServiceCustomerTypeCode=''S''

2. av.AuctionID = (SELECT MAX(AuctionVehicle.AuctionID) FROM AuctionVehicle WHERE AuctionVehicle.VehicleContractID IN ('+@VehicleCode+'))

3. AND VS.ServiceSettlePrice<>0

这三条和连接无关，只是一些过滤的条件，所以一定要加到 where里而不是放到on里

innner join的时候因为是严格的连接，所以on里放一些过滤条件是不会被忽略的。

转自：http://beijiguang-fred.blog.sohu.com/153417642.html