query-the-size-of-postgres-array.md

Query the Size of Postgres Array

Today I learned how to query the size of a Postgres array. There are (at least) two methods that work.

The first is array_length. This requires you to know the array dimension you seek; a useful filter, although most of the time this will probably be 1:

hr-til_development=# select title from posts
hr-til_development=# where array_length(slack_notified_at_likes_threshold, 1) = 1;
                   title
-------------------------------------------
 Because Javascript
 Percent Notation
 DIY Grids for Designing UI in Illustrator
(3 rows)

When the dimension is 1, a more terse solution is cardinality:

hr-til_development=# select title from posts
hr-til_development=# where cardinality(slack_notified_at_likes_threshold) = 1;
                   title
-------------------------------------------
 Because Javascript
 Percent Notation
 DIY Grids for Designing UI in Illustrator
(3 rows)

Documentation