MySQL: SUM of a column based on a value of another column

Question

I want to have a sum of a column that is based if the value of another column is this/that. Here's my table structure

id  leave_hours leave_type overtime_hours employee_id
1     7.6          1           0               3
2      5           2           0               3
3      0           0           2.3             3

I have this query already but I need to have a column that will only sum if leave type is 1 and if the leave type is 2

SELECT employee_id, SUM(overtime_hours) AS ot_hrs, SUM(leave_hours if leave_type == 1) AS  
       leave_1, SUM(leave_hours if leave_type == 2) AS leave_2
FROM table
GROUP BY employee_id

Result should be:

employee_id  ot_hrs leave_1  leave_2
    3          2.3    7.6       5

Thanks for your inputs.

Answer 1

You need to use conditional aggregation to sum the different leave_hours separately:

SELECT employee_id, 
       SUM(overtime_hours) AS ot, 
       SUM(CASE WHEN leave_type = 1 THEN leave_hours ELSE 0 END) AS leave_1, 
       SUM(CASE WHEN leave_type = 2 THEN leave_hours ELSE 0 END) AS leave_2
FROM `table`
GROUP BY employee_id

Output:

employee_id ot      leave_1     leave_2
3           2.3     7.6         5

Demo on dbfiddle

Note that if you use floating point numbers to store the hours, you may need to ROUND the results.

Answer 2

you can use max() with case when

SELECT employee_id, 
       max(overtime_hours) AS ot, 
       max(CASE WHEN leave_type = 1 THEN leave_hours  END) AS leave_1, 
       max(CASE WHEN leave_type = 2 THEN leave_hours END) AS leave_2
FROM  table_name
GROUP BY employee_id

output

employee_id     ot     leave_1       leave_2
3              2.3  7.599999904632568   5