I have 3 database tables as follows:
projects:
id
project_name
project_location
status
project_expenses
id
project_id
expense_category
expense_subcategory
amount
userid
date
payment_status
project_status
project_income
id
project_id
project_income
date
userid
project_status
projects.id, project_expenses.project_id and project_income.project_id are related.
I need to create a query displaying Project_ID,Project_Name,SUM of Project_Income,SUM of Project_expenses
I tried the following query but not getting correct result.
SELECT p.id AS id, p.project_name AS project_name, SUM(i.project_income) AS income, SUM(e.amount) AS expenses
FROM project_income i, project_expenses e, projects p
WHERE i.project_id = p.id AND e.project_id = p.id AND p.status = 'Active'
GROUP BY id
I have currently 2 rows in project_income and 4 rows in project_expenses. The result is project_income displays double the values. Something is wrong with my JOIN.
Being a newbie I am unable to understand what i am doing wrong?? Requesting help...
Use sub-selects in the query result columns. No need for GROUP BY.
SELECT p.id
, p.project_name
, ( SELECT SUM(i.project_income)
FROM project_income i
WHERE i.project_id = p.id
) AS income
, ( SELECT SUM(e.amount)
FROM project_expenses e
WHERE e.project_id = p.id
) AS expenses
FROM projects p
WHERE p.status = 'Active'
The problem with the query in the question is best explained with an example.
You say there are 2 rows in project_income and 4 rows in project_expenses. Let say the 2 incomes are 1000 and 1500, and the 4 expenses are 615, 750, 840, and 900.
Since there are no restrictions between them, that means you'll get the cross join, i.e. 8 records:
income expense
1000 615
1000 750
1000 840
1000 900
1500 615
1500 750
1500 840
1500 900
Now, when you sum income you get 4 times the value you want, and when you sum expense you get 2 times the value you want.