MySQL multiple tables conditional filter - mysql

Question

I want to check the validity of a user_id, from a table of users that contains three types of users (type i, c and p).
For users of type c to be valid, the current user.party_id has to be present in the customer_partner table against the supplied $PNR.
For users of type i to be valid, the current user.party_id has top be present in the installer_partner table against the supplied $PNR.
For users of type p to be valid, the current user.party_id has to be the supplied $PNR.
I want the returned row to be the user details if valid, or no rows if invalid. I have tried a couple of ways to do this, but unsuccessfully.
EXAMPLE 1: I am using a CASE in the select then placing a v or e value in the resulting column, then filtering out in the WHERE statement, but this gives me Unknown column 'valid_user' in 'where clause' error.
SELECT
CASE users.party_type
WHEN 'c'
THEN IF(users.party_id IN (SELECT pnrcus.customer_id
FROM customer_partner AS pnrcus
WHERE pnrcus.partner_id = '.$PNR.'),'v','e')
WHEN 'i'
THEN IF(users.party_id IN (SELECT pnrins.installer_id
FROM installer_partner AS pnrins
WHERE pnrins.partner_id = '.$PNR.'),'v','e')
WHEN 'p'
THEN IF(users.party_id = '.$PNR.','v','e')
ELSE 'e'
END AS valid_user,
users.email_user_id,
users.party_id,
users.person_id,
users.first_name,
users.last_name
FROM users AS users
WHERE LCASE(users.email_user_id) = LCASE('.$UID.')
AND users.password = '.$PWD.'
AND valid_user = 'v'
AND users.account_status = 'a'
EXAMPLE 2: I am using OR statements in the WHERE part of the sql. This returns the wrong rows.
SELECT
users.party_type
users.email_user_id,
users.party_id,
users.person_id,
users.first_name,
users.last_name
FROM users AS users
WHERE LCASE(users.email_user_id) = LCASE('.$UID.')
AND users.password = '.$PWD.'
AND users.account_status = 'a'
AND (
parties.party_type = 'c'
AND users.party_id IN (SELECT pnrcus.customer_id
FROM sma_customer_partner AS pnrcus
WHERE pnrcus.partner_id = .$PNR.')
) OR (
parties.party_type = 'i'
AND users.party_id IN (SELECT pnrins.installer_id
FROM sma_installer_partner AS pnrins
WHERE pnrins.partner_id = .$PNR.')
) OR (
parties.party_type = 'p'
AND users.party_id = '.$PNR.'
)

Answer 1

A quick fix to your problem is to add a HAVING clause for the column in the resultset you created:
SELECT
CASE users.party_type
WHEN 'c'
THEN IF(users.party_id IN (SELECT pnrcus.customer_id
FROM customer_partner AS pnrcus
WHERE pnrcus.partner_id = '.$PNR.'),'v','e')
WHEN 'i'
THEN IF(users.party_id IN (SELECT pnrins.installer_id
FROM installer_partner AS pnrins
WHERE pnrins.partner_id = '.$PNR.'),'v','e')
WHEN 'p'
THEN IF(parties.party_id = '.$PNR.','v','e')
ELSE 'e'
END AS valid_user,
users.email_user_id,
users.party_id,
users.person_id,
users.first_name,
users.last_name
FROM users AS users
WHERE LCASE(users.email_user_id) = LCASE('.$UID.')
AND users.password = '.$PWD.'
AND users.account_status = 'a'
HAVING valid_user = 'v'
But, frankly, I'd do this:
SELECT
users.party_type
users.email_user_id,
users.party_id,
users.person_id,
users.first_name,
users.last_name
FROM users AS users
LEFT JOIN customer_partner AS pnrcus
ON pnrcus.partner_id = '.$PNR.'
AND pnrcus.customer_id = users.party_id
AND users.party_type = 'c'
LEFT JOIN installer_partner AS pnrins
ON pnrins.partner_id = '.$PNR.'
AND pnrins.installer_id = users.party_id
AND pnrins.party_type = 'i'
WHERE
LCASE(users.email_user_id) = LCASE('.$UID.')
AND users.password = '.$PWD.'
AND users.account_status = 'a'
AND (
( users.party_type ='p' AND users,party_id = '.$PNR.' )
OR pnrcus.partner_id IS NOT NULL
OR pnrins.partner_id IS NOT NULL
)
GROUP BY users.email_user_id;
Note BTW that this is very slow:
LCASE(users.email_user_id) = LCASE('.$UID.')
You might want to use a collation where 'A'='a' == true (all _ci ones are), or store it lowercase, and provide it lowercase. As it stands it cannot use an index.