Question

MySQL: How to count rows when multiple joined tables ??

+Query:

    SELECT p.role FROM users u 
    INNER JOIN roles r ON r.id=u.role 
    INNER JOIN permissions p ON p.role=r.id 
    WHERE p.p_id=19 AND p.p_update=1 AND r.active=1 
    GROUP BY p.role

+Result:

    ________
    |p_role:|
    |_______|
    |   1   |
    |   4   |
    |_______|

When I add COUNT() function to p.role:

+Query:

    SELECT COUNT(p.role) FROM users u 
    INNER JOIN roles r ON r.id=u.role 
    INNER JOIN permissions p ON p.role=r.id 
    WHERE p.p_id=19 AND p.p_update=1 AND r.active=1 
    GROUP BY p.role

+Result:

    _______________
    |COUNT(p_role):|
    |______________|
    |      5       |
    |      1       |
    |______________|

Why I see 2 records I already use COUNT() function??
I don't want to see result like this.
I want to count rows of query above.

I want to see result like this:

    _______________
    |COUNT(p_role):|
    |______________|
    |      2       |
    |______________|

Please anyone help me. Thanks in advance!
Sorry for my broken English.

Answer 1

由于查询中包含GROUP BY子句，它会返回每p.role个值的计数。如果您希望查询返回一个值，则可以删除GROUP BY，例如：

SELECT COUNT(DISTINCT(p.role)) FROM users u 
INNER JOIN roles r ON r.id=u.role 
INNER JOIN permissions p ON p.role=r.id 
WHERE p.p_id=19 AND p.p_update=1 AND r.active=1;

顺便说一句，我已将DISTINCT添加到查询中，以便它返回不同p.role值的计数。如果您只想记录记录，可以删除DISTINCT。

MySQL：如何在多个连接表时计算行数？

1 个答案: