LEFT JOIN with exceptions - mysql

Question

Here's my current query:
$q = "SELECT u.uid,CONCAT_WS(' ', u.first_name, u.last_name) name, CASE WHEN t.name IS NULL THEN 0 ELSE t.name END AS teamname ";
$q .= "FROM {$users} ";
$q .= "LEFT JOIN {$schedule} ON u.uid = s.uid ";
$q .= "LEFT JOIN {$products} ON p.admitting_id = u.uid ";
$q .= "LEFT JOIN {$teams} ON t.id = s.team ";
$q .= "WHERE (u.uid = {$current_user_id} AND u.roles = 'hoa') OR ";
$q .= "(p.id={$pid} AND p.admitting_id != 0) OR ";
$q .= "(t.admitting = 1 AND s.inactive != 1 AND s.role = 'hoa' AND (s.date = '{$today}' OR (s.date = '{$yesterday}' AND t.overnight = 1))) ";
$q .= "ORDER BY u.last_name,u.first_name,t.name";
What I need to get is:
Current User, if Current User has role hoa
User where uid matches admitting_id from products table
All users with role hoa who are scheduled today or were scheduled yesterday on an overnight shift. With those scheduled users, I need the names of the team they were/are scheduled with. Duplicate uids is good because I need all the different team names if they were scheduled on multiple teams.
What I don't need to get is:
Team name for options 1 and 2 above.
What I'm getting is:
Everything perfect for #3 above.
All possible team names for #1 and #2 above, whereas I want the team names to be 0 if they're not on the schedule.
I could split this up into three queries but that's not preferable.

Answer 1

Sometimes formatting the query out a bit helps visualise. It doesn't need to become three queries, I agree.
Can you provide some sample schema and data, ideally both in the question description and on something like sqlfiddle for us to play with?
It's hard to visualise your structure and data, but I'm speculating the issue is every record in users table is joining to schedule with the on clause you've used.
You could move the logic of condition 3 into the on clause (it's a left join, so nothing else will break) or duplicate it in the CASE statement in the SELECT:
$q = <<<SQL
SELECT
u.uid,
CONCAT_WS(' ', u.first_name, u.last_name) name,
IF(
WHEN t.name IS NULL THEN
0
ELSE
t.name
END AS teamname
FROM {$users} AS u
LEFT JOIN {$schedule} AS s ON (u.uid = s.uid)
LEFT JOIN {$products} AS p ON (p.admitting_id = u.uid)
LEFT JOIN {$teams} AS t ON
(
t.id = s.team AND
t.admitting = 1 AND
s.inactive != 1 AND
s.role = 'hoa' AND
(
s.date = '{$today}'
OR
(
s.date = '{$yesterday}' AND
t.overnight = 1
)
)
)
WHERE
( -- 1: Current User, if Current User has role hoa
u.uid = {$current_user_id} AND
u.roles = 'hoa'
)
OR
( -- 2: User where uid matches admitting_id from products table
p.id={$pid} AND
p.admitting_id != 0
)
OR
t.name IS NOT NULL
ORDER BY
u.last_name,
u.first_name,
t.name
SQL;
I'm absolutely not certain that'll fix your problem without something real to play with... Happy to continue looking if you can provide a working example sandpit.