Question

I’ve got a MySQL table with about 100,000 records. When I try to select about 20 rows from this table using the primary key (an unsigned int) it takes about a second to execute. Is there any way to optimise this?

Table: films

Column          Type        Null    Default 
film_id         int(11)     No       
film_name       varchar(45) No       
film_overview   text        No       
film_tagline    varchar(150)Yes     NULL     
release_date    date        Yes     NULL     
api_id          int(11)     No       
category_id     int(11)     No      0 

Indexes on films

Keyname         Type    Unique  Packed  Column      Cardinality Collation   Null    Comment
PRIMARY         BTREE   Yes     No      film_id     110236      A           No  
api_id          BTREE   No      No      api_id      110236      A           No  
film_id         BTREE   No      No      film_id     110236      A           No  
category_id     BTREE   No      No      category_id 4           A           No  

EXPLAIN

id  select_type         table           type    possible_keys   key     key_len     ref     rows    Extra
1   PRIMARY             films           ALL     NULL            NULL    NULL        NULL    115029  Using where
2   DEPENDENT SUBQUERY  popular_films   ALL     NULL            NULL    NULL        NULL    18      Using where

QUERY

SELECT film_name FROM `films` 
  WHERE film_id in (SELECT film_id FROM popular_films); 

Answer 1

Now that you’ve added the query, the answer is simple: just use a join:

SELECT films.film_name
FROM `films`
JOIN popular_films
  ON popular_films.film_id = films.film_id;

It looks like your popular_films table has the same structure as films, and so probably shouldn’t be a separate table.