SELECT supplierID,(case when defaultsupplierid is null then supplierId else supplierId+'default' end) as test FROM tblsupplier A LEFT JOIN tblproductVariant B ON A.SUPPLIERID=
B.defaultSupplierID
case when then else end的功能是:
case when (條件是否爲真) 如果是真執行 then 後面的語句,如果是假執行else後面的語句 end結束