Laravel query builder join after where clause - php

Question

I am using laravel 8. I have this mysql command which I want to convert into laravel query builder style:
select allocation.*, leav_leave_types.leave_type_code
from (
select * from leav_employee_annual_leave_allocations
where leave_year_id = $year_id and employee_id = $user_id
) as allocation
left join leav_leave_types on (leav_leave_types.id = allocation.leave_type_id)
Actually I want to apply a where clause first and then perform a left join for better performance.
How can I convert it into query builder style?

Answer 1

The only thing from your query that is not currently in the documentation is using a subquery as the main table.
This can be done by passing either a Closure or a Builder instance to the table() or from() method.
DB::table(closure, alias)
DB::table(builder, alias)
DB::query()->from(closure, alias)
DB::query()->from(builder, alias)
Using a Closure:
DB::table(function ($sub) use ($user_id, $year_id) {
$sub->from('leav_employee_annual_leave_allocations')
->where('leave_year', $year_id)
->where('employee_id', $user_id);
}, 'allocation')
->select('allocation.*', 'leav_leave_types.leave_type_code')
->leftJoin('leav_leave_types', 'leav_leave_types.id', 'allocation.leave_type_id')
->get();
DB::query()
->select('allocation.*', 'leav_leave_types.leave_type_code')
->from(function ($sub) use ($user_id, $year_id) {
$sub->from('leav_employee_annual_leave_allocations')
->where('leave_year', $year_id)
->where('employee_id', $user_id);
}, 'allocation')
->leftJoin('leav_leave_types', 'leav_leave_types.id', 'allocation.leave_type_id')
->get();
Using a Builder instance
$sub = DB::table('leav_employee_annual_leave_allocations') // or DB::query()->from('leav_employee_annual_leave_allocations')
->where('leave_year', $year_id)
->where('employee_id', $user_id);
DB::table($sub, 'allocation')
->select('allocation.*', 'leav_leave_types.leave_type_code')
->leftJoin('leav_leave_types', 'leav_leave_types.id', 'allocation.leave_type_id')
->get();
// personally my favorite way. I find it very readable.
$sub = DB::table('leav_employee_annual_leave_allocations') // or DB::query()->from('leav_employee_annual_leave_allocations')
->where('leave_year', $year_id)
->where('employee_id', $user_id);
DB::query()
->select('allocation.*', 'leav_leave_types.leave_type_code')
->from($sub, 'allocation')
->leftJoin('leav_leave_types', 'leav_leave_types.id', 'allocation.leave_type_id')
->get();
The generated SQL looks like this
select "allocation".*, "leav_leave_types"."leave_type_code" from (
select * from "leav_employee_annual_leave_allocations"
where "leave_year" = ? and "employee_id" = ?
) as "allocation"
left join "leav_leave_types" on "leav_leave_types"."id" = "allocation"."leave_type_id"
If you want a parenthesis around your join condition to be generated, you should use one of the following notations instead.
leftJoin('leav_leave_types', ['leav_leave_types.id' => 'allocation.leave_type_id'])
leftJoin('leav_leave_types', function ($join) {
$join->on(['leav_leave_types.id' => 'allocation.leave_type_id']);
})
leftJoin('leav_leave_types', function ($join) {
// will generate a parenthesis if there's more than one condition
$join->on('leav_leave_types.id', 'allocation.leave_type_id')
->on(...) // and condition
->orOn(...); // or condition
})

Answer 2

Alternatively, you could turn the SQL around to
select *,
( SELECT leave_type_code
FROM leav_leave_types
WHERE id = allocation.leave_type_id
) AS leave_type_code
FROM leav_employee_annual_leave_allocations AS allocation
where leave_year_id = $year_id and employee_id = $user_id
(This might be more efficient.)
In either case leav_employee_annual_leave_allocations would benefit from INDEX(employee_id, leave_year_id).