UNION in MYSQL and merge columns - php

Question

I am fetching data from two tables in mysql. I have query like this:
SELECT SUM(IF(debit IS NULL, 0, debit)) - SUM(IF(credit IS NULL, 0, credit)) as amount, th.country_id, cl.currency_name
FROM account_treasury_hq th
LEFT JOIN system_country_list cl ON cl.country_id=th.country_id
WHERE th.company_id='$company_id'
GROUP BY th.country_id
UNION
SELECT SUM(CASE WHEN ce_type = 'IN' or ce_type is NULL then payment_amount
WHEN ce_type = 'OUT' then - payment_amount
END) as amount,
source_country_id as country_id, cl.currency_name
FROM customer_payment_options cpo
LEFT JOIN system_country_list cl ON cl.country_id=cpo.source_country_id
WHERE cpo.company_id='$company_id'
GROUP BY cpo.source_country_id
Result
Array
(
[0] => Array
(
[amount] => -345
[country_id] => 40
[currency_name] => Canadian dollar
)
[1] => Array
(
[amount] => 93
[country_id] => 210
[currency_name] => Sri Lankan rupee
)
[2] => Array
(
[amount] => 46.5
[country_id] => 236
[currency_name] => United States dollar
)
[3] => Array
(
[amount] => 916249.8999999999
[country_id] => 40
[currency_name] => Canadian dollar
)
[4] => Array
(
[amount] => -6670.1
[country_id] => 210
[currency_name] => Sri Lankan rupee
)
[5] => Array
(
[amount] => 2017.67
[country_id] => 236
[currency_name] => United States dollar
)
)
In the result array, you can see the same country_id. I want to merge those same country id with 1. It means, there should only be each amount information for each country_id.
(amount should be added by adding multiple countries)
Is there any way to do it in PHP or mysql itself?
Thanks for any kind of help.
Required Result
Array
(
[0] => Array
(
[amount] => 915904.89
[country_id] => 40
[currency_name] => Canadian dollar
)
[1] => Array
(
[amount] => -6577.1
[country_id] => 210
[currency_name] => Sri Lankan rupee
)
[2] => Array
(
[amount] => 2064.17
[country_id] => 236
[currency_name] => United States dollar
)
)

Answer 1

just select it all in an outer query sum the amount and group by country_id
SELECT
SUM(amount) country_id, currency_name
FROM
( SELECT
SUM(IF(debit IS NULL, 0, debit)) - SUM(IF(credit IS NULL, 0, credit)) as amount,
th.country_id,
cl.currency_name
FROM account_treasury_hq th
LEFT JOIN system_country_list cl ON cl.country_id=th.country_id
WHERE th.company_id='$company_id'
GROUP BY th.country_id
UNION
SELECT
SUM(CASE
WHEN ce_type = 'IN' or ce_type is NULL then payment_amount
WHEN ce_type = 'OUT' then - payment_amount
END
) as amount,
source_country_id as country_id,
cl.currency_name
FROM customer_payment_options cpo
LEFT JOIN system_country_list cl ON cl.country_id=cpo.source_country_id
WHERE cpo.company_id='$company_id'
GROUP BY cpo.source_country_id
) t
GROUP BY country_id

Answer 2

You're doing a union, with grouping in the individual subquery. Each subquery in a union has NO awareness of what the other parallel queries are doing. Each query's group by will apply only to that ONE query.
You'd need to do the heavy duty work in a wrapper query, e.g.
SELECT SUM(.....)
FROM (
SELECT th.country_id AS country_id, etc...
UNION ALL
SELECT source_country AS country_id, etc...
) AS foo
GROUP BY country_id
e.g. do all the grouping and "math" in the outer query, and the inner queries simply retrieve all the records you do want grouped together.

Answer 3

Didn't test this (would need a sqlfiddle to play with) but you'd want to aggregate them in the query. Something like this (you'll want to tweak the group by and select for your needs):
SELECT SUM( x.amount ), x.country_id, x.currency_name
FROM
(
SELECT SUM(IF(debit IS NULL, 0, debit)) - SUM(IF(credit IS NULL, 0, credit)) as amount, th.country_id, cl.currency_name
FROM account_treasury_hq th
LEFT JOIN system_country_list cl ON cl.country_id=th.country_id
WHERE th.company_id='$company_id'
GROUP BY th.country_id
UNION
SELECT SUM(CASE WHEN ce_type = 'IN' or ce_type is NULL then payment_amount
WHEN ce_type = 'OUT' then - payment_amount
END) as amount,
source_country_id as country_id, cl.currency_name
FROM customer_payment_options cpo
LEFT JOIN system_country_list cl ON cl.country_id=cpo.source_country_id
WHERE cpo.company_id='$company_id'
GROUP BY cpo.source_country_id
) AS x
GROUP BY x.amount, x.country_id, x.currency_name