php - Count and IN Clause Issue

Question

I have a table named as employee history and its structure is as follows.

tbl_employee_history Structure

id|history_nr|history_value|employee_id
1   82         83             1
2   86         84             1 
3   87         85             1
4   603                       1
5   82         83             2
6   86         83             2
7   87         83             2
8   603        83             2

This is the dummy data for my table. Now I want to count all those employees whose history_nr is in 82,86,87,603 AND history_value should not be empty like in the above example the count should be 1 as for employee id 2 all the values are not empty. This is my query for implementing the count.

SELECT count(employee_id) FROM tbl_employee_history where history_nr IN(82,86,87,603) AND history_value!=''

But what happens is the count returns me two values. Thanks in advance.

Answer 1

删除您distinct()的查询部分，这将只返回唯一值。由于 1 和 2 各有 4 行employee_id，因此它只会抓取具有 distinct (unique) 的第一行employee_id。

因此它只提取 2 条记录，每条记录 1 条employee_id。

SELECT count(employee_id) FROM tbl_employee_history where history_nr IN(82,86,87,603) AND history_value != ''
//Returns 7 Rows

SELECT count(distinct(employee_id)) FROM tbl_employee_history where history_nr IN(82,86,87,603) AND history_value != ''
//Returns 2 Rows