Mysql query with Left Join is too very slow

Question

Query:

   select `r`.`id` as `id` 
     from `tbl_rls` as `r` 
left join `tblc_comment_manager` as `cm` on `cm`.`rlsc_id` != `r`.`id`

Both tabl

Answer 1

Looks like you are wanting the r.id values that are not in the tblc_comment_manager table.

Use a Not In

select r.id as id
from tbl_rls as r
where r.id not in (select distinct cm.rlsc_id from tblc_comment_manager as cm)