Issue with adding fields of multiple tables - php

Question

I have three tables with same structure.
table1
id | email | count
1 | test1#abc.com | 5
2 | test2#abc.com | 5
3 | test3#abc.com | 5
table2
id | email | count
1 | test1#abc.com | 50
2 | test1#abc.com | 50
3 | test3#abc.com | 50
table3
id | email | count
1 | test1#abc.com | 40
2 | test1#abc.com | 45
3 | test1#abc.com | 50
Now what i want is for table1, for first record "test1#abc.com", I need sum of "count" field of next two tables. So i used below query
SELECT (IFNULL(sum(distinct(table2.count)), 0) +
IFNULL(sum(distinct(table3.count)), 0)) as total
FROM table1
LEFT JOIN table2 ON table1.email = table2.email
LEFT JOIN table3 ON table1.email = table3.email
WHERE table1.email = 'test1#abc.com'
This query gives me below record:
185
But the result should be as below:
235
This is because i have used distinct when adding field. But if i don't use distinct, it gives me 285.
Please help. What should i do?

Answer 1

Your issue is because, first, you're using LEFT JOIN (no sense with summation since NULL-records will provide nothing), second, that's how JOIN works. Illustrate with query:
SELECT
t1.id AS id_1,
t1.email AS email_1,
t1.count AS count_1,
t2.id AS id_2,
t2.email AS email_2,
t2.count AS count_2,
t3.id AS id_3,
t3.email AS email_3,
t3.count AS count_3
FROM
table1 AS t1
INNER JOIN table2 AS t2 ON t1.email=t2.email
INNER JOIN table3 AS t3 ON t1.email=t3.email
WHERE
t1.email='test1#abc.com'
(fiddle is here). As you can see, you'll get repeated id's from second and third tables - and - yes, that's because there are multiple rows for joining condition.
To resolve your issue you may add distinction by id into join (and later filtering that with variables or like that), but I would not recommend it. JOIN is simply not the thing for your issue. Use UNION, like:
SELECT
SUM(`count`) AS s
FROM
(
SELECT
table2.count
FROM
table2
WHERE
email='test1#abc.com'
UNION ALL
SELECT
table3.count
FROM
table3
WHERE
email='test1#abc.com'
) AS u
(see the fiddle)