如何獲得1983年1月1日以后加入的部門明智員工的人數

Question

假設我有這張桌子：

+-----+------+------------+
| eid | dept | joining    |
+-----+------+------------+
|   1 | IT   | 1982-01-13 |
|   2 | IT   | 1983-01-13 |
|   3 | CSE  | 1984-04-13 |
|   4 | CSE  | 1983-03-23 |
|   5 | IT   | 1985-03-23 |
|   6 | ECE  | 1986-03-23 |
|   7 | ECE  | 1986-11-23 |
+-----+------+------------+

現在，我想獲取1983年1月1日以后加入的每個部門的雇員人數記錄。

我試過這個查詢：

select count(a.eid) as total, dept
from (
    select *
    from t1
    where dept = 'IT'
    having DATE(joining) > '1982-01-01'
) as a;

+-------+------+
| total | dept |
+-------+------+
|     3 | IT   |
+-------+------+

但是我需要所有部門在一張桌子里。

select joining, dept, count(*)
from t1
group by dept
having(joining) > '1982-01-01'
order by joining;

沒有這樣的結果。

Answer 1

您需要一個簡單的group by子句，並在其中過濾所需的日期，例如：

select dept,count(*)
from t1
where joining > '1982-01-01' 
group by dept

Answer 2

having子句是應用於由group by子句創建的group by 。 您需要使用一個簡單的where子句，該子句將條件分別應用於每一行：

SELECT   dept, COUNT(*)
FROM     t1
WHERE    joining > '1982- 01-01'
GROUP BY dept

Answer 3

您是否嘗試過僅將日期移動到WHERE子句中，而不是將其放入GROUP BY中，例如：

SELECT joining, dept, count(*)
FROM t1
WHERE joining > '1982-01-01'
GROUP BY dept
ORDER BY joining ACS;