PostgreSQL has an SOME operator that is used to compare a scalar value with a set of values returned by a subquery.
Syntax: expression operator SOME(subquery)
The below rules must be followed while using PostgreSQL SOME operator:
- The subquery must return exactly one column.
- The SOME operator must be preceded by one of the following comparison operator =, <=, >, <, > and <>
- The SOME operator returns true if any value of the subquery meets the condition, otherwise, it returns false.
For the sake of this article we will be using the sample DVD rental database, which is explained here and can be downloaded by clicking on this link in our examples.
Here we will query for the maximum length of film grouped by film category from the “film” table of our sample database.
SELECT title FROM film WHERE length >= SOME( SELECT MAX( length ) FROM film INNER JOIN film_category USING(film_id) GROUP BY category_id );
Here we will query for the films whose category is either Action(category_id = 1) or Drama(category_id = 7) from the “category” table of our sample database.
SELECT title, category_id FROM film INNER JOIN film_category USING(film_id) WHERE category_id = SOME( SELECT category_id FROM category WHERE NAME = 'Action' OR NAME = 'Drama' );