Is there any difference between these two performance-wise?
-- eliminate duplicates using UNION
SELECT col1,col2,col3 FROM Table1
UNION SELECT col1,col2,col3 FROM Table2
UNION SELECT col1,col2,col3 FROM Table3
UNION SELECT col1,col2,col3 FROM Table4
UNION SELECT col1,col2,col3 FROM Table5
UNION SELECT col1,col2,col3 FROM Table6
UNION SELECT col1,col2,col3 FROM Table7
UNION SELECT col1,col2,col3 FROM Table8
-- eliminate duplicates using DISTINCT
SELECT DISTINCT * FROM
(
SELECT col1,col2,col3 FROM Table1
UNION ALL SELECT col1,col2,col3 FROM Table2
UNION ALL SELECT col1,col2,col3 FROM Table3
UNION ALL SELECT col1,col2,col3 FROM Table4
UNION ALL SELECT col1,col2,col3 FROM Table5
UNION ALL SELECT col1,col2,col3 FROM Table6
UNION ALL SELECT col1,col2,col3 FROM Table7
UNION ALL SELECT col1,col2,col3 FROM Table8
) x
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