MySQL LEFT JOIN query is very slow - mysql

Question

SELECT bi.id,
bi.location,
bi.expense_group,
bi.level,
bi.is_active,
bi.type,
full_name,
Sum(DISTINCT bl.amount) AS
BudgetAmount,
Sum(DISTINCT Ifnull(( bl.amount * 6 ) - ( + bal1.amount + bal2.amount +
bal3.amount
+ bal4.amount + bal5.amount +
bal6.amount ), 0)) AS
Difference,
Sum(DISTINCT Ifnull(Round(( + bal1.amount + bal2.amount + bal3.amount
+ bal4.amount + bal5.amount + bal6.amount ) /
6), 0)
) AS Average,
Sum(DISTINCT bal1.amount) AS BAL1,
Sum(DISTINCT bal2.amount) AS BAL2,
Sum(DISTINCT bal3.amount) AS BAL3,
Sum(DISTINCT bal4.amount) AS BAL4,
Sum(DISTINCT bal5.amount) AS BAL5,
Sum(DISTINCT bal6.amount) AS BAL6
FROM (SELECT *
FROM budget_items
WHERE bi.location IS NOT NULL) AS bi
LEFT JOIN budget_lines AS bl
ON bi.id = bl.budget_item_id
AND bl.budget_id = 5983
LEFT JOIN balance_lines AS bal1
ON bi.id = bal1.budget_item_id
AND bal1.balance_id = 28839
LEFT JOIN balance_lines AS bal2
ON bi.id = bal2.budget_item_id
AND bal2.balance_id = 28633
LEFT JOIN balance_lines AS bal3
ON bi.id = bal3.budget_item_id
AND bal3.balance_id = 26664
LEFT JOIN balance_lines AS bal4
ON bi.id = bal4.budget_item_id
AND bal4.balance_id = 14500
LEFT JOIN balance_lines AS bal5
ON bi.id = bal5.budget_item_id
AND bal5.balance_id = 10199
LEFT JOIN balance_lines AS bal6
ON bi.id = bal6.budget_item_id
AND bal6.balance_id = 7204
GROUP BY bi.id
ORDER BY bi.position
As you can see actually there are only 3 tables, but I need to query one of them for each of the balances.
This is taking a lot of time. Where is my mistake?
After struggling with #Gordon Linoff post, I tried to fix it myself. #Gordon Linoff is that what you meant?
SELECT bi.id,
bi.location,
bi.expense_group,
bi.level,
bi.is_active,
bi.type,
full_name,
(bl.bud_amount) AS BudgetAmount,
(coalesce(( bl.bud_amount * 6 ) - (bal.bal_amount1 + bal.bal_amount2 + bal.bal_amount3 + bal.bal_amount4 + bal.bal_amount5 + bal.bal_amount6),
0)) AS Difference,
(coalesce(Round(( bal.bal_amount1 + bal.bal_amount2 + bal.bal_amount3 + bal.bal_amount4 + bal.bal_amount5 + bal.bal_amount6 ) /
6), 0)
) AS Average,
bal.bal_amount1 AS BAL1,
bal.bal_amount2 AS BAL2,
bal.bal_amount3 AS BAL3,
bal.bal_amount4 AS BAL4,
bal.bal_amount5 AS BAL5,
bal.bal_amount6 AS BAL6
FROM (SELECT *
FROM budget_items bi
WHERE bi.location IS NOT NULL
) AS bi
LEFT JOIN
(select budget_item_id, Sum(case when budget_id = 5983 then amount end) AS bud_amount
from budget_lines
group by budget_item_id
) AS bl
on bl.budget_item_id = bi.id
JOIN
(select budget_item_id,
IFNULL(Sum(case when balance_id = 28839 then amount end), 0) AS bal_amount1,
IFNULL(Sum(case when balance_id = 28633 then amount end), 0) AS bal_amount2,
IFNULL(Sum(case when balance_id = 26664 then amount end), 0) AS bal_amount3,
IFNULL(Sum(case when balance_id = 14500 then amount end), 0) AS bal_amount4,
IFNULL(Sum(case when balance_id = 10199 then amount end), 0) AS bal_amount5,
IFNULL(Sum(case when balance_id = 7204 then amount end), 0) AS bal_amount6
from balance_lines
group by budget_item_id
) AS bal
on bal.budget_item_id = bi.id
ORDER BY bi.location

Answer 1

Whenever you have sum(distinct . . . ) you have a problem. You are getting cartesian products on the left outer join, and your overall results will not be accurate if there are two lines that have the same amount.
I think you want to replace all those left outer join with a subquery like this:
select budget_item_id,
Sum(case when budget_id = 5983 then amount end) AS BAL,
Sum(case when budget_id = 28839 then amount end) AS BAL1,
Sum(case when budget_id = 28633 then amount end) AS BAL2,
Sum(case when budget_id = 26664 then amount end) AS BAL3,
Sum(case when budget_id = 14500 then amount end) AS BAL4,
Sum(case when budget_id = 10199 then amount end) AS BAL5,
Sum(case when budget_id = 7204 then amount end) AS BAL6
from balance_lines
group by budget_item_id
and then fix the rest of the query.
Here is an attempt to write the query. This undoubtedly has syntax errors:
SELECT bi.id,
bi.location,
bi.expense_group,
bi.level,
bi.is_active,
bi.type,
full_name,
(bl.bal) AS BudgetAmount,
(coalesce(( bl.bal * 6 ) - (bl.bal1 + bl.bal2 + bl.bal3 + bl.bal4 + bl.bal5 + bl.bal6),
0)) AS Difference,
(coalesce(Round(( bl.bal1 + bl.bal2 + bl.bal3 + bl.bal4 + bl.bal5 + bl.bal6 ) /
6), 0)
) AS Average,
bl.bal1 AS BAL1,
bl.bal2 AS BAL2,
bl.bal3 AS BAL3,
bl.bal4 AS BAL4,
bl.bal5 AS BAL5,
bl.bal6 AS BAL6
FROM (SELECT *
FROM budget_items bi
WHERE bi.location IS NOT NULL
) bi left outer join
(select budget_item_id,
Sum(case when budget_id = 5983 then amount end) AS BAL,
Sum(case when budget_id = 28839 then amount end) AS BAL1,
Sum(case when budget_id = 28633 then amount end) AS BAL2,
Sum(case when budget_id = 26664 then amount end) AS BAL3,
Sum(case when budget_id = 14500 then amount end) AS BAL4,
Sum(case when budget_id = 10199 then amount end) AS BAL5,
Sum(case when budget_id = 7204 then amount end) AS BAL6
from balance_lines
group by budget_item_id
) bal
on bal.budget_item_id = bi.id
ORDER BY bi.position
Note that I entirely removed the outer group by, assuming that bi.id is a unique key on the budget items table.