根据列值动态决定连接表

Question

I want to dynamically inner join tables, here is my SQL query

Update temp
Set temp.Order_Id = parent.ID

from #TempTransactions AS temp

Inner Join (case when temp.OrderType = 1 then preorders else orders end)  AS parent

ON parent.Cloud_Id = temp.Order_Id

Is it possible I can decide in above way or any other alternative?

If yes, how?

Answer 1

Two Left joins would do.

Update temp Set temp.Order_Id = COALESCE(p.ID, o.ID)

from #TempTransactions AS temp

LEFT Join preorders p ON p.Cloud_Id = temp.Order_Id AND temp.OrderType=1
LEFT JOIN orders o ON o.Cloud_Id = temp.Order_Id AND (temp.OrderType <> 1 OR temp.OrderType IS NULL)
WHERE COALESCE(p.ID, o.ID) IS NOT NULL