如何获得1983年1月1日以后加入的部门明智员工的人数

Question

Suppose I have this table:

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

Now I want to get the records of number of employees in each department who joined after 1st January, 1983.

I tried this query:

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

But I need all departments in one table.

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

No such result.

Answer 1

You need a simple group by clause with a where that filters the dates you want, like this:

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

Answer 2

The having clause is a condition applied on the groups created by the group by clause. You need to use a simple where clause which applies the condition to each row individually:

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

Answer 3

Have you tried simply just moving your date into a WHERE clause, instead of having it in the GROUP BY, like this:

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