另一个表中存在的sql查询条目

Question

I have two tables: requests ( email ) , results ( email , data , processed_at )

I want to get an entry from results that has processed_at = null and an email which exists in requests . My current approach is to use a join :

select `results`.* from `results` 
inner join `requests` on `requests`.`email` = `results`.`email` 
where `results`.`processed_at` is null limit 1

Unfortunately this is very slow. Is there a more efficient way to do this?

Answer 1

You could also use a subquery like:

SELECT results.*
FROM results
WHERE results.processed_at IS NULL
    AND results.mail IN (SELECT DISTINCT requests.mail FROM requests)
LIMIT 1

However, I'm not sure if it's faster.

Answer 2

can you try this query

select

res .* from

results res, requests req

where req . email = res . email

and res . processed_at is null

Answer 3

select results .* from results left join requests on requests . email = results . email where results . processed_at is null limit 1

i am quite sure that this is much faster than inner join.