Query shows values from tables differently [duplicate] - mysql

Question

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sql sum data from multiple tables
(6 answers)
Closed 2 years ago.
I have 3 tables (attendance, allowances and deductions) with some records in attendance.Wage, allowances.Amount, deductions.Amount columns. And I want to "SUM" values in these columns with selected date.
Summed up values must be
attendance.Wage:100
allowances.Amount:150
deductions.Amount:120
but with my query values are seeing very different.
SELECT Name, SUM(attendance.Wage), SUM(allowances.Amount), SUM(deductions.Amount) FROM employees
INNER JOIN attendance USING (EmployeeID)
INNER JOIN allowances USING (EmployeeID)
INNER JOIN deductions USING (EmployeeID)
WHERE MONTH(attendance.Date) = 6 AND YEAR(attendance.Date) = 2020
AND
MONTH(allowances.Date) = 6 AND YEAR(allowances.Date) = 2020
AND
MONTH(deductions.Date) = 6 AND YEAR(deductions.Date) = 2020
GROUP BY employees.EmployeeID;
Output of the query:
attendance.Wage:400
allowances.Amount:900
deductions.Amount:720
Why the values are multiplying or increasing? How can I fix that?

Answer 1

Because you are getting multiple rows from each table and the join is multiplying them.
Without additional information, I would recommend correlated subqueries:
SELECT e.Name,
(SELECT SUM(a.Wage)
FROM attendance a
WHERE a.EmployeeID = e.EmployeeID AND
a.date >= '2020-06-01' AND a.date < '2020-07-01'
),
(SELECT SUM(a.Amount)
FROM allowances a
WHERE a.EmployeeID = e.EmployeeID AND
a.date >= '2020-06-01' AND a.date < '2020-07-01'
),
(SELECT SUM(d.Amount)
FROM deduction d
WHERE d.EmployeeID = e.EmployeeID AND
d.date >= '2020-06-01' AND d.date < '2020-07-01'
)
FROM employees e;
With an index on (EmployeeId, date, amount/wage) in each of the three tables, this should also have better performance than alternatives using explicit aggregations and joins.

Answer 2

You would need to push the aggregation down in subqueries, otherwise the sums count each value multiple times.
SELECT e.Name, ad.total_attendance, aw.total_allowances, dd.total_deductions
FROM employees e
INNER JOIN (
SELECT EmployeeID, SUM(wage) total_attendance
FROM attendance
WHERE date >= '2020-06-01' and date < '2020-07-01'
GROUP BY EmployeeID
) ad USING (EmployeeID)
INNER JOIN (
SELECT EmployeeID, SUM(amount) total_allowances
FROM allowances
WHERE date >= '2020-06-01' and date < '2020-07-01'
GROUP BY EmployeeID
) aw USING (EmployeeID)
INNER JOIN (
SELECT EmployeeID, SUM(amount) total_deductions
FROM deductions
WHERE date >= '2020-06-01' and date < '2020-07-01'
GROUP BY EmployeeID
) dd USING (EmployeeID)