if exists(Select 1 from Sclass where BnameId in (select Bid from Bclass where Bname='电脑设备'))
Select Sname from Sclass where BnameId in (select Bid from Bclass where Bname='电脑设备')
Select Sname from Sclass where BnameId in (select Bid from Bclass where Bname='电脑设备')
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