How to use cross join with left outer join? - mysql

Question

I have to show list of employee who has claim for expense for the particular month, but am getting all employee list.
SELECT employee_id, expense_month, GROUP_CONCAT(CONCAT_WS('=', exp_type_text, monthly_exployee_expense))
FROM
(
SELECT tbl_employee.employee_id, expense_months.expense_month, tbl_expense_type.exp_type_id, tbl_expense_type.exp_type_text, SUM(expense_cost) AS monthly_exployee_expense
FROM tbl_employee
CROSS JOIN tbl_expense_type
CROSS JOIN
(
SELECT DISTINCT DATE_FORMAT(expense_date, '%Y%m') AS expense_month
FROM exp_tbl
) expense_months
LEFT OUTER JOIN exp_tbl
ON tbl_employee.employee_id = exp_tbl.employee_id
AND tbl_expense_type.exp_type_id = some_table.expense_type
AND expense_months.expense_month = DATE_FORMAT(exp_tbl.expense_date, '%Y%m')
GROUP BY tbl_employee.employee_id, expense_months.expense_month, tbl_expense_type.exp_type_id, tbl_expense_type.exp_type_text
) Sub1
GROUP BY employee_id, expense_month
this the query i had.. how to get only expense claimed employee list.
Example out put is:
3 Ramesh Kumar M 201402 Phone Expense=0=16,Consumable Purchase=0=11,Auto=0...
3 Ramesh Kumar M 201403 Consumable Purchase=0=11,Auto=0=6,2 wheeler=0=1,Lo...
3 Ramesh Kumar M 201404 Logistics/Transportation=0=18,Labour=0=13,Fuel=0=8...
3 Ramesh Kumar M 201405 Bus Travel=0=3,Office Vehicle=0=20,Others=0=15,Sta...
4 testexplevel1 201402 Others=0=15,Stay=0=10,Train Travel=0=5,Office Main...
4 testexplevel1 201403 Office Maintenance=0=17,Billable Purchase=0=12,Cal...
4 testexplevel1 201404 Call Taxi=0=7,4 wheeler=0=2,Guest House=0=19,Trans...
In that list not want all employee list. Only show ramesh data. Because that employee only has claimed.

Answer 1

Makes sense. You cross join all employees against all months and all expense types into a big cartesian product. Then you left join the actual expenses, so nothing gets excluded if there are no expenses.
So the quick fix would be to inner join the expenses. Doing so only gives you the employee-months for which an expense exists.
But doing so also allows you to remove the cross joins altogether and change it all to inner joins:
select
emp.employee_id,
DATE_FORMAT(ex.expense_date, '%Y%m'),
GROUP_CONCAT(CONCAT_WS('=', et.exp_type_text, ex.monthly_exployee_expense))
from
tbl_employee emp
inner join exp_tbl ex on ex.employee_id = emp.employee_id
inner join tbl_expense_type et on et.exp_type_id = ex.expense_type
group by
emp.employee_id,
DATE_FORMAT(ex.expense_date, '%Y%m')
Now, isn't that query much cleaner? :)