Using UNION to add selected field in multiple select statements? (1 reply)

Hi all. I'm hoping that someone might help me with what I think needs to be a UNION statement. I've got 4 different SELECT statements that all return a DECIMAL amount. I need to add the first two sums and subtract the second two sums and return the answer. This answer will actually be a sub-query used in a INSERT statement.

# returns 9.15
SELECT sum( a.amount ) AS amount
FROM `transactions` AS p
INNER JOIN `transactions` AS a
INNER JOIN `parents` AS r ON ( r.parentID = p.id
AND r.childID = a.id )
WHERE p.userID = 4
AND p.acctID = 1;

# returns 5.50
SELECT sum( amount )AS aAmount FROM `transactions` WHERE userID = 4 AND acctID = 1;

# returns 5.50
SELECT sum( a.amount ) AS tsAmount
FROM `transactions` AS p
INNER JOIN `transactions` AS a
INNER JOIN `parents` AS r ON ( r.parentID = p.id
AND r.childID = a.id )
WHERE p.userID =4
AND a.catID =1
AND a.type = 'transfer';

# returns 5.50
SELECT sum( amount )AS tAmount FROM `transactions` WHERE userID = 4 AND catID = 1 AND type='transfer';

Here's my best attempt at using a UNION statement for this.
SELECT (aSplit.amount + a.amount - tSplit.amount - t.amount) from (

# returns 9.15
(SELECT sum( a.amount ) AS amount
FROM `transactions` AS p
INNER JOIN `transactions` AS a
INNER JOIN `parents` AS r ON ( r.parentID = p.id
AND r.childID = a.id )
WHERE p.userID = 4
AND p.acctID = 1) AS aSplit;

UNION DISTINCT

# returns 5.50
(SELECT sum( amount )AS aAmount FROM `transactions` WHERE userID = 4 AND acctID = 1) as a;

UNION DISTINCT

# returns 5.50
(SELECT sum( a.amount ) AS tsAmount
FROM `transactions` AS p
INNER JOIN `transactions` AS a
INNER JOIN `parents` AS r ON ( r.parentID = p.id
AND r.childID = a.id )
WHERE p.userID =4
AND a.catID =1
AND a.type = 'transfer') AS tSplit;

UNION DISTINCT

# returns 5.50
(SELECT sum( amount )AS tAmount FROM `transactions` WHERE userID = 4 AND catID = 1 AND type='transfer') AS t;
)