How To improve a sql query performance - sql

Question

I Have a view that return to me the customers and sum of their payment and its work but it take 8 second and when i remove the computed column part from the query it didn't take any time, and i tried to solve this by creating a non-clustered index on tables but its also 8 second, so I'm asking about if there is any method to improve the performance, although i have to use this technique.
my code is
SELECT ID
,NAME
,Total = (
SELECT Sum(Value)
FROM TRANSACTION
WHERE Employee.ID = employee_ID
)
FROM Employee;
Thanks in advance

Answer 1

You could use a join in the subselect with the sum
select e.id, e.name, t.total
from employee e
join (
select employee_ID, sum(value) as total
from TRANSACTION
group by employee_ID
) t on t.employee_ID = e.id

Answer 2

You can try to use a join with group and see if that is faster:
select employee.id, employee.name, sum(value)
from employee
join transaction where transaction.employee_ID = employee.id
group by employee.id, employee.name
Also - try to avoid to give names that correspond to reserved words - like TRANSACTION - see https://dev.mysql.com/doc/refman/5.5/en/keywords.html
To hasten up you might want to consider a combined index on Emlpoyee(id,name) AND an index on Transaction.Employee_ID - both are neede to make the joins and grouping for this query fast. Check if transaction.employee_ID has a FK_Constraint to Employee.ID - that might help as well.

Answer 3

For this query:
SELECT ID, NAME,
(SELECT Sum(t.Value)
FROM TRANSACTION t
WHERE e.Employee.ID = t.employee_ID
) as Total
FROM Employee e;
You want an index on TRANSACTION(employee_ID, Value). That should actually give you optimal performance.
You can write this as a join -- but a left join:
SELECT e.ID, e.NAME, SUM(t.Value) as Total
FROM Employee e JOIN
TRANSACTION t
ON e.Employee.ID = t.employee_ID
GROUP BY e.ID, e.NAME;
However, the overall GROUP BY is usually less efficient than the "sub group by" in MySQL (and often in other databases as well).

Answer 4

Try an indexed view on the total
CREATE VIEW totalView
WITH SCHEMABINDING
AS
select employee_ID, sum(value) as total
from TRANSACTION
group by employee_ID
CREATE UNIQUE CLUSTERED INDEX PK_totalView ON totalView
(
employee_id,total
);
Then join to that
select employee.id, employee.name, coalesce(t.total,0)
from employee
left outer join totalView t where t.employee_ID = employee.id
Adjust the join type according to your need.