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  1.  Home
  2. JAVA400-L
  3. November 2007

RE: Suggestion with SQL query

From: Joe Pluta

SELECT t1.id, t1.type, COALESCE(t2.value, t1.value)
FROM t1 LEFT OUTER JOIN t2 ON t1.id = t2.id and t1.type = t2.type

That ought to do the trick. Basically, if there is a row in T2, t2.value
will be used. Otherwise, t2.value will be NULL and t1.value will be used.

Nothing against Michael's UNION technique, either, this technique just seems
a little more straightforward to me. But that's the thing about SQL; there
are often several ways to do the same thing, and the performance of each
technique may be influenced by the data in the files.

Joe


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