php - mysql select union 不起作用

Question

Mysql 版本 5.1。代码示例:

mysql_query("SELECT * FROM abonents WHERE `session_id`='$current_sess_id' UNION SELECT * FROM abonents_problem WHERE `session_id`='$current_sess_id' UNION SELECT * FROM abonents_stop WHERE `session_id`='$current_sess_id'");

如果删除“UNION”则运行，示例:

mysql_query("SELECT * FROM abonents WHERE `session_id`='$current_sess_id'" );

“WTF 代码”永远=):

$rez_11_one = mysql_query(
        "SELECT * FROM abonents WHERE `session_id`='$current_sess_id'"
    );
    $rez_11_two = mysql_query(
        "SELECT * FROM abonents_problem WHERE `session_id`='$current_sess_id'"
    );
    $rez_11_three = mysql_query(
        "SELECT * FROM abonents_stop WHERE `session_id`='$current_sess_id'"
    );
    if ($rez_11_one) {
        $rez_11 = $rez_11_one;
    } elseif ($rez_11_two) {
        $rez_11 = $rez_11_two;
    } else {
        $rez_11 = $rez_11_three;
    }

谢谢你的帮助

Answer 1

对 mysql 文档的引用 UNION 仅在所有查询返回相同数量的 columns 时才有效。

http://dev.mysql.com/doc/refman/4.1/en/union.html

因此，当您使用选择器星号 * 时，我认为这些表具有不同数量的列。使用 select 例如

SELECT 1,2 FROM foo UNION SELECT 1,2 FROM bar

为每个查询获取相同数量的列。