选择一个表相对于其他两个表不存在的行？

Question

I have three tables I am trying to build a query against in Eloquent to get only the rows from two tables that are absent from a third table.

One is the table histories which references the other two tables schedules and templates . If there is a template schedule history, I don't want to get that schedule.

Normally I would expect this could be done using a LEFT JOIN on the third table where the id IS NULL but this doesn't work in this instance. Every query I have tried thus far always returns the null columns along with the row I don't want.

Here is a fiddle with the relevant schema and an example query: http://sqlfiddle.com/#!2/28aad/5

How can I structure my query to get the results desired?

Answer 1

Your query should look like this: However your query is not returning any results because each schedule/template has a history record.

select 
    histories . *,
    histories.id as 'history_id',
    schedules . *,
    schedules.id as 'schedule_id'
from
    schedules
left join
    histories ON schedules.id = histories.schedule_id
        and schedules.template_id = histories.template_id
where
    schedules.schedulable_id = 16
    and schedules.schedulable_type = 'Item'
    and histories.id IS NULL

Answer 2

Assuming you wish to get rows for schedules table which are not in histories table, your eloquent query would be such:

//Fetches list of schedule IDs from Histories table
$schedule_ids = Histories::distinct()->lists('schedule_id')
//Get list of all schedules which are not present in Histories table
$queryresult = Schedules::WhereNotIn('id', $schedule_ids)->get();`

Answer 3

select 
    schedules . *,
    schedules.id as 'schedule_id',
    histories . *,
    histories.id as 'history_id'
from
    schedules
left join
    histories ON schedules.id = histories.schedule_id
        and schedules.template_id = histories.template_id
where
    histories.id IS NOT NULL
;

This lists schedules IDs 1 & 2

select 
    schedules . *,
    schedules.id as 'schedule_id',
    histories . *,
    histories.id as 'history_id'
from
    schedules
left join
    histories ON schedules.id = histories.schedule_id
        and schedules.template_id = histories.template_id
where
    histories.id IS NULL
;

This lists schedule ID 3 , but this does not match other conditions such as

• schedules.schedulable_id = 16

see: http://sqlfiddle.com/#!2/28aad/21