java - 如何获取 1983 年 1 月 1 日之后加入的部门员工数量

Question

假设我有这张表:

+-----+------+------------+
| 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 |
+-----+------+------------+

现在我想获取1983年1月1日之后加入的每个部门的员 worker 数记录。

我尝试了这个查询:

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   |
+-------+------+

但我需要将所有部门放在一张表中。

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

没有这样的结果。

Answer 1

您需要一个简单的 group by 子句，其中包含一个 where 来过滤您想要的日期，如下所示:

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