Slow MySQL queries using SUM()

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.