mysql - 如何在 MySQL 中限制查询中的字段

Question

我有两个这样的表:

TableOne(id, name, attr)
{
    1, Mark, A
    2, Peter, B
    3, John, A
    4, Mary, A
}
TableTwo(id, id_TableOne, path)
{
    1, 1, one.png
    2, 1, two.png
    3, 1, three.png
    4, 3, foo.png
    5, 3, bar.png
}

SELECT TableOne.name, TableTwo.path
FROM TableOne, TableTwo
WHERE TableOne.attr = 'A'
AND TableOne.id = TableTwo.id_TableOne

That outputs:

{
    Mark, one.png
    Mark, two.png
    Mark, three.png
    John, foo.png
    John, bar.png
}

我想限制子查询，每个名称只显示一个路径。 所需的输出将是:

{
    Mark, one.png
    John, foo.png
    Mary, NULL
}

我尝试做 LIMITS，并在另一个中写一个 select，但我没有得到我想要的结果，我还读到一些让我担心的东西

"MySQL does not support LIMIT in subqueries for Un Certain subquery operators"

来自 http://dev.mysql.com/doc/refman/5.0/en/subquery-restrictions.html

谁能指导我解决我的问题？请。

Answer 1

试试这个:

SELECT TableOne.name, MIN(TableTwo.path)
FROM TableOne LEFT JOIN TableTwo ON (TableOne.id = TableTwo.id_TableOne)
WHERE TableOne.attr = 'A'
GROUP BY TableOne.name