「UNION」の使い方がイマイチわからないので、検索してたら、
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[ { UNION [ ALL ] | INTERSECT | EXCEPT } select ]
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というものを見つけ、いちかばちか UNION ALL にしてみたら、動きました!
( SELECT * FROM i24_job WHERE job_print_open >= '$svndysago' ORDER BY job_print_open DESC ) UNION ALL ( SELECT * FROM i24_job WHERE job_print_open < '$svndysago' order by job_urgent_flag DESC job_print_open DESC )
【1】SELECT * FROM i24_job WHERE job_print_open >= '2004-10-03' ORDER BY job_print_open DESC
【2】SELECT * FROM i24_job WHERE job_print_open < '2004-10-03' order by job_urgent_flag DESC job_print_open DESC
(SELECT * FROM i24_job WHERE job_print_open >= '2004-10-03' ORDER BY job_print_open DESC) UNION (SELECT * FROM i24_job WHERE job_print_open < '2004-10-03' order by job_urgent_flag DESC job_print_open DESC)
SELECT * FROM i24_job WHERE job_print_open >= '2004-10-03' ORDER BY job_print_open DESC
SELECT * FROM i24_job WHERE job_print_open < '2004-10-03' AND job_urgent_flag = '1' order by job_print_open DESC
SELECT * FROM i24_job WHERE job_print_open < '2004-10-03' AND job_urgent_flag = '0' order by job_print_open DESC