if statements in SQL view

I have an sql view with 3 tables which I have described the basic layout of below. I want to create a view to show the main table with the address. If the column [External] has Yes in it, then I want to pull the address from the external table, if the value is no then I want to pull it from the internal table. Is this easy enough to do? Any examples would be appreciated.



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Jim HornMicrosoft SQL Server Data DudeCommented:
Give this a whirl..
Replace 'Yes' and 'No' with 1 and 0 if it's a bit field, and '???' with whatever floats your boat
SELECT tm.ID, tm.Name, 
   CASE cm.External
      WHEN 'Yes' THEN te.address1
      WHEN 'No' THEN ti.address1
      ELSE '???' END as address1, 
   CASE cm.External
      WHEN 'Yes' THEN te.address2
      WHEN 'No' THEN ti.address2
      ELSE '???' END as address2, 
   CASE cm.External
      WHEN 'Yes' THEN te.address3
      WHEN 'No' THEN ti.address3
      ELSE '???' END as address3
FROM TableMain tm
   LEFT JOIN TableInternal ti ON tm.LinkID = ti.LinkID
   LEFT JOIN TableExternal te ON tm.LinkID = te.LinkID

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Vitor MontalvãoMSSQL Senior EngineerCommented:
Try this:
SELECT M.ID, M.Name, M.External, E.Address1, E.Address2, E.Address3
FROM TableMain M
	INNER JOIN TableExternal E ON M.LinkID = E.LinkID
WHERE External='YES'
SELECT M.ID, M.Name, M.External, I.Address1, I.Address2, I.Address3
FROM TableMain M
	INNER JOIN TableInternal I ON M.LinkID = I.LinkID
WHERE External='NO'

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Scott PletcherSenior DBACommented:
SELECT m.ID, m.name,
    COALESCE(i.Address1, e.Address1) AS Address1,
    COALESCE(i.Address2, e.Address2) AS Address2,
    COALESCE(i.Address3, e.Address3) AS Address3
FROM TableMain m
LEFT OUTER JOIN TableInternal i ON m.[External] = 'No'  AND i.LinkID = m.ID
LEFT OUTER JOIN TableExternal e ON m.[External] = 'Yes' AND e.LinkID = m.ID
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