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.
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