Question

让我们说mysql就是这样的

select x,y 
from xx 
group by y

我想知道选择了多少行，我试图使用count但是它不会返回所有结果，因为我正在使用group by。

怎么做？

由于

Answer 1

您可以像这样包装您的查询：

SELECT COUNT(*) FROM
  (select x,y  
    from xx  
    group by y) sub;

Answer 2

假设您有一个包含以下内容的表格：

 -------------------
| ID | NAME | GROUP |
+-------------------+
| 1  |  A   |  1    |
+-------------------+
| 2  |  B   |  2    |
+-------------------+
| 3  |  C   |  2    |
+-------------------+
| 4  |  D   |  3    |
+-------------------+
| 5  |  E   |  1    |
+-------------------+
| 6  |  F   |  3    |
+-------------------+

以下自我LEFT JOIN计算GROUP中不同值的数量。

SELECT COUNT(*)
FROM table AS t1
LEFT JOIN table AS t2 ON t2.GROUP = t1.GROUP AND t2.ID > t1.ID
WHERE t2.id IS NULL;

此查询的作用是为每个组找出id最高的元素。

Answer 3

您可以查看我的https://stackoverflow.com/a/36449637/2439715

SELECT 
    sum(1) as counttotal
FROM (
    Your query with group by operator
) as T

mysql group by和count rows问题

3 个答案: