mysql_query UNION循环

Question

我如何使用循环执行与下面脚本相同的操作？

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$res = mysql_query("SELECT * FROM {$table_1} WHERE txn_id LIKE '%{$txn_id}%'
					UNION
					SELECT * FROM {$table_2} WHERE txn_id LIKE '%{$txn_id}%'
					UNION
					SELECT * FROM {$table_3} WHERE txn_id LIKE '%{$txn_id}%'
					UNION
					SELECT * FROM {$table_4} WHERE txn_id LIKE '%{$txn_id}%'
					UNION
					SELECT * FROM {$table_5} WHERE txn_id LIKE '%{$txn_id}%'

＆＃13;

＆＃13;

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感谢。