Question

I am having issues with an InnoDB mysql database. E.g., I have two tables, events and events_artists with the following architecture:

events:
id (PK)
host_id
date

events_artists:
id (PK)
event_id
artist_id

The table events has about 100,000 entries, events_artists holds about 150,000.

One of the things I have to do is check for entries in the table events that are not referred to in the table events_artists. To do that, in another post I have received the query

SELECT * FROM events WHERE id IS NULL OR id NOT IN (SELECT event_id FROM events_artists)

From the logic, this query looks good to me. However, it is just extremely slow. I let it run for one hour now, and still no result. Something has to be wrong there.

I am grateful for any help on how to optimize this!

Thanks

Charles

SOLUTION FOUND

The following query makes the statement much faster:

SELECT * 
FROM events a
     LEFT JOIN events_artists b
     ON a.id = b.event_id
     WHERE b.event_id IS NULL;

However, the main speed boost was adding foreign keys. I had to remove them in the interim for some duplicate search and added them back now, which increases speed a lot. While the query took more than an hour before, it only takes one second now.

Thank you!

Charles

Answer 1

To get faster results you should avoid using sub-query. Alternatively you can try using LEFT JOIN to get records which are in events but not in events_artists.

Visit Visual explanation of joins

SELECT * 
FROM events a
     LEFT JOIN events_artists b
         ON a.id = b.event_id
WHERE b.event_id IS NULL;

Also make sure that you have index on columns id and event_id for faster query execution.