Problems with UNION and ORDER BY

[steve ralph]

Hi I am trying to merge 2 database tables If I leave out the ORDER BY clause I get results from the first table. If anyone can help with the correct syntax it would be much appreciated. The code is as follows.

$query = "(SELECT CONCAT(a_item1) AS i1, (a_item2) AS i2, (a_item3) AS i3, DATE_FORMAT(db1.tbl1.tbl_date, '%M %d, %Y') AS tm FROM db1.tbl1, db1.tbl2 WHERE status = '6' AND tbl1_ID = tbl2_ID ORDER BY db1.tbl1.tbl_date DESC LIMIT 12)
UNION ALL
SELECT CONCAT(b_item1) AS i1, (b_item2) AS i2, (b_item3) AS i3, DATE_FORMAT(db2.tbl1.tbl_date, '%M %d, %Y') AS tm FROM db2.tbl1, db2.tbl2 WHERE status = '6' AND tbl1_ID = tbl2_ID ORDER BY db2.tbl1.tbl_date DESC LIMIT 12) LIMIT 6";

$result = mysql_query ($query); // Run the query

if ($result){

If I place

ORDER BY tbl_date DESC

before the last "LIMIT 6"
I do not get any results out.

Lots of thanks
Steve