计算不同的值

Question

resulttable：

+-------------+-----------+
| resultSetID | projectID |
+-------------+-----------+
|           1 |         1 |
|           1 |         2 |
|           1 |         3 |
|           2 |         1 |
|           2 |         2 |
|           3 |         1 |
|           3 |         2 |
|           3 |         3 |
+-------------+-----------+

查询：

SELECT
    COUNT( projectID ) 
FROM
    resulttable
WHERE
    projectID = 3

...正确返回2.但是，我想要不使用WHERE条件的每个ID的计数，我该怎么做？

Answer 1

你只想要group by吗？

SELECT projectId, COUNT( * ) 
FROM resulttable
GROUP BY projectID;

Answer 2

以下查询用于获取projectId的所有数据，但如果您想获取不包含where的特定查询数据，则可以使用instead

SELECT projectId, COUNT( * ) 
FROM resulttable
GROUP BY projectId having projectId = 3;

Answer 3

以下查询适合您：

SELECT projectID, SUM(resultSetID) 
FROM resulttable
GROUP BY projectID;