MySQL 5.5.24-log 更新查询连接

Question

在数据库MySQL版本5.5.24-log中，我有两个表tbl_t1和 tbl_t2。

这些表有共同的关键区域。

这是如此，因为如果尝试此连接查询，输出是正确的:

mysql> SELECT
    areat2,
    areat1,
    nameareat1,
    monthareat2
FROM
    tbl_t1 t1
JOIN tbl_t2 t2 ON t1.areat1 = t2.areat2
WHERE
    monthareat2 = '2014-08'
GROUP BY
    t1.areat1
ORDER BY
    t1.nameareat1 ASC;
+--------+--------+-----------------------+-------------+
| areat2 | areat1 | nameareat1            | monthareat2 |
+--------+--------+-----------------------+-------------+
| XX4M   | XX4M   | AREA AAAAAA           | 2014-08     |
| XX5M   | XX5M   | AREA BBBBBB           | 2014-08     |
| XX4N   | XX4N   | AREA CCCCCC           | 2014-08     |
| XX1M   | XX1M   | AREA DDDDDD           | 2014-08     |
+--------+--------+-----------------------+-------------+
4 rows in set

现在，当存在两个表的键区域时，我需要更新表tbl_t1中的字段valid .

我尝试过这个解决方案，但出现错误。

UPDATE tbl_t1 t1
JOIN (
    SELECT
    areat2,
    areat1,
    nameareat1,
    monthareat2
    FROM
        tbl_t1 t1
    JOIN tbl_t2 t2 ON t1.areat1 = t2.areat2
    WHERE
        monthareat2 = '2014-08'
    GROUP BY
        t1.areat1
) AS t2 ON t1.areat1 = t2.areat2
SET t1.valid = 1;

[Err] 1060 - Duplicate column name 'areat1'

你能解释一下这是怎么做的吗？

提前谢谢您。

Answer 1

在内部和外部查询中使用不同的别名:

UPDATE tbl_t1 t3
JOIN (
    SELECT
    areat2,
    areat1,
    nameareat1,
    monthareat2
    FROM
        tbl_t1 t1
    JOIN tbl_t2 t2 ON t1.areat1 = t2.areat2
    WHERE
        monthareat2 = '2014-08'
    GROUP BY
        t1.areat1
) AS t4 ON t3.areat1 = t4.areat2
SET t3.valid = 1;