How to find the size of an array in postgresql

As vyegorov mentioned, array_length will do the trick. Or if you know that the array is 1-dimensional (which is likely) and are running PostgreSQL 9.4 or higher, you can use cardinality:

SELECT cardinality(id) FROM example;

It's trivial reading docs:

SELECT array_length(id, 1) FROM example;

Assuming the dimension of the array will always be 1 isn't something I feel comfortable with, so I went with the following:

SELECT coalesce(array_length(id, 1), 0) as size FROM example;

It's been... at least a decade, but we used to do a lot with coalesce and it was pretty handy. Maybe I'm reaching for it out of comfort?

Had to use array_upper in postgres 8.2.