Making my mysql query more efficient - mysql

Question

What I am trying to do is pulling the id,phone_type,os_version columns from Enswitch_Mobile_Users table.
And with the id i've just got to get the enswitch_id from Enswitch_Users table.
And after that to COUNT all the entires from Enswitch_Android_Purchases or Enswitch_Iphone_Purchases which the user colum match the id from enswitch_mobile_users. and getting first entry date and the last entry date.
And I managed to made it work with this query:
SELECT p.user AS `Mobile_User_ID`,
e.os_version `Os_Version`,
e.phone_type `Phone_Type`,
eu.enswitch_id `Enswitch_ID`,
Count(1) AS `Buy_Count`,
(SELECT pc.date
FROM
(
SELECT date, user, status
FROM enswitch_android_purchases
UNION
SELECT date, user, status
FROM enswitch_iphone_purchases
) AS pc
WHERE pc.status = 1
AND pc.user = p.user
ORDER BY pc.date ASC
LIMIT 1) AS `First_Purchase`,
(SELECT pc.date
FROM
(
SELECT date, user, status
FROM enswitch_android_purchases
UNION
SELECT date, user, status
FROM enswitch_iphone_purchases
) AS pc
WHERE pc.status = 1
AND pc.user = p.user
ORDER BY pc.date DESC LIMIT 1) AS `Last_Purchase`
FROM
(
SELECT item, date, user, status
FROM enswitch_android_purchases
UNION
SELECT item, date, user, status
FROM enswitch_iphone_purchases
) AS p
LEFT JOIN enswitch_mobile_users e
ON p.user = e.id
LEFT JOIN enswitch_users eu
ON e.user_id = eu.id
WHERE p.`date` >= :from_date
AND p.`date` <= :to_date
AND p.user is not null
AND p.status = 1
GROUP BY `Mobile_User_ID`
But because of the selects it will be really slow so how can I make it more efficient?

Answer 1

You might be able to use the following which replaces the two selects in the SELECT list with min(p.date) and max(p.date):
SELECT p.user AS `Mobile_User_ID`,
e.os_version `Os_Version`,
e.phone_type `Phone_Type`,
eu.enswitch_id `Enswitch_ID`,
Count(1) AS `Buy_Count`,
min(p.date) AS `First_Purchase`,
max(p.date) AS `Last_Purchase`
FROM
(
SELECT item, date, user, status
FROM enswitch_android_purchases
UNION
SELECT item, date, user, status
FROM enswitch_iphone_purchases
) AS p
LEFT JOIN enswitch_mobile_users e
ON p.user = e.id
LEFT JOIN enswitch_users eu
ON e.user_id = eu.id
WHERE p.`date` >= :from_date
AND p.`date` <= :to_date
AND p.user is not null
AND p.status = 1
GROUP BY p.user