MySQL中多表不关联查询

MySQL中多表不关联查询
多表不关联查询中，需要在结果数组中区分开每张表所查询出来的数据，在每个子SELET语句中加入固定值再加以判断。
问题解决...
语句：
(SELECT field1 AS a,field11 AS b, '常量1' AS c FROM table1) UNION ALL (SELECT field2 AS a,field22 AS b, '常量2' AS c FROM table2)  UNION ALL ... ORDER BY a DESC

结果：
Array
(
    [0] => Array
        (
            [a] => ...
            [b] => ...
            [c] => '常量1'
        )

    [1] => Array
        (
            [a] => ...
            [b] => ...
            [c] => '常量1'
        )

    [2] => Array
        (
            [a] => ...
            [b] => ...
            [c] => '常量2'
        )
  
    [3] => Array
        (
            [a] => ...
            [b] => ...
            [c] => '常量1'
        )
)