Slow MySQL queries using SUM() - mysql

Question

I have to run two queries in my code to get my tenants balance. However, these queries are too slow.
First query, I get all the tenants and it's unit name:
SELECT t.TenantID
FROM Tenants t
JOIN Units u
ON t.UnitID = u.UnitID
Where t.Prospect = 2
AND t.PropertyID = 8
ORDER
BY CONCAT(Left(Replace(UnitName,'-',''),2),
REPEAT('0', (10-CHAR_LENGTH(UnitName))),
Right(Replace(UnitName,'-',''),
CHAR_LENGTH(Replace(UnitName,'-',''))-2
) )
It returns 500 rows
Then I get the balances in 4 conditions. This query will be inside of first query loop:
Select
SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) AS TotalDebit,
SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) AS HousingDebit,
SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) AS TotalCredit,
SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) AS HousingCredit
From TenantTransactions
Where TenantID= FirstQuery.TenantID
Am I doing the queries wrong? It's taking like 1 minute to run.

Answer 1

Do this in a single query with GROUP BY.
Try something like this:
SELECT t.TenantID, TotalDebit, HousingDebit, TotalCredit, HousingCredit
FROM Tenants t
JOIN Units u ON t.UnitID = u.UnitID
LEFT JOIN (
Select
TenantID,
SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) AS TotalDebit,
SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) AS HousingDebit,
SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) AS TotalCredit,
SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) AS HousingCredit
From TenantTransactions
Group By TenantID
) sums ON sums.TenantID = t.TenantID
Where t.Prospect = 2
AND t.PropertyID = 8
ORDER
BY CONCAT(Left(Replace(UnitName,'-',''),2),REPEAT('0', (10-CHAR_LENGTH(UnitName))),Right(Replace(UnitName,'-',''),CHAR_LENGTH(Replace(UnitName,'-',''))-2))
The inner query may still run for a while but it will only run once.
Try a compound covering index on TenantTransactions containing these columns: (TenantID, TransactionTypeID, ChargeTypeID, TransactionAmount) to optimize the query with the SUMs in it.
Try a compound index on Tenants with the columns (PropertyID, Prospect) in it.

Answer 2

Here's another way to do it with a subquery. You know, the performance problem might not be database performance, but the back and forth between your database and application server. So that is where a single query will help.
SELECT t.TenantID,
(SELECT SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) From TenantTransactions TT WHERE TT.TenantID=t.TenantID) AS TotalDebit,
(SELECT SUM(CASE WHEN TransactionTypeID = 1 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) From TenantTransactions TT WHERE TT.TenantID=t.TenantID) AS HousingDebit,
(SELECT SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID != 6 THEN TransactionAmount ELSE 0 END) From TenantTransactions TT WHERE TT.TenantID=t.TenantID) AS TotalCredit,
(SELECT SUM(CASE WHEN TransactionTypeID = 2 AND ChargeTypeID = 6 THEN TransactionAmount ELSE 0 END) From TenantTransactions TT WHERE TT.TenantID=t.TenantID) AS HousingCredit
FROM Tenants t
JOIN Units u
ON t.UnitID = u.UnitID
Where t.Prospect = 2
AND t.PropertyID = 8
ORDER
BY CONCAT(Left(Replace(UnitName,'-',''),2),REPEAT('0', (10-CHAR_LENGTH(UnitName))),Right(Replace(UnitName,'-',''),CHAR_LENGTH(Replace(UnitName,'-',''))-2))