join多张表（包含判断）
1 select tm.*,tmt.MTType,tp.PollingName ,tam.AcqModelType,tb.BRType,tp.PollingName, ta.AcquisitionName ,ta.AcquisitionId,ta.AcquisitionAddr,tt.terminalid,tt.TerminalName,tt.commuaddr 2 from tb_meter tm join tb_Acquisition ta join tb_Terminal tt 3 on tt.TerminalId=ta.TerminalId 4 on ta.AcquisitionId=tm.AcquisitionId 5 left join dbo.tb_MeterType tmt on tmt.MTId=tm.MeterType 6 left join dbo.tb_BaudRate tb on tb.BRId=tm.BaudRate 7 left join dbo.tb_Polling tp on tp.PollingId= case when tm.Polling>7 then 7 else tm.Polling end 8 left join dbo.tb_AcqModel tam on tam.AcqModelId=tm.Model
蓝色部分是重点，当id>=7的时候，显示id为7的字段。
