獲取不同值的計數

Question

結果表：

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

查詢：

SELECT
    COUNT( projectID ) 
FROM
    resulttable
WHERE
    projectID = 3

...正確返回2。但是，我希望不使用WHERE條件就對每個ID進行計數，我該怎么做？

Answer 1

您只想group by嗎？

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

Answer 2

下面的查詢是用來獲取的所有數據projectId ，但如果你想沒有一個具體的查詢數據where ，你可以使用具有instead

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

Answer 3

以下查詢將為您工作：

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