Array overlaps an array in Postgres

user_4957288 0
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I'm making a search by tags function, in a table like this

    CREATE TABLE permission (
      id serial primary key,
      tags varchar(255)[],
    );

Then I add a row that has the tags "artist" and "default".

I'd like to query it by tags (using the knex query builder), so if I do this:

  async getByTags(tags: string[]): Promise<PermissionTable[]> {
    return this.db<PermissionTable>('permission')
      .select('*')
      .whereRaw("tags @> '{??}'", [tags])
  }

That produces the following statements depending on how many tags you passed.

This works

    select * from "permission" where tags @> '{"artist"}';

This doesn't (returns an empty array, when it should the row I'm looking for)

    select * from "permission" where tags @> '{"artist", "event"}';

Why does the one with multiple tags not work?

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1 Answers

@> is the "contains" operator so a1 @> a2 is true when a1 contains all the elements in a2. For example:

array['artist', 'default'] @> array['artist']            -- True
array['artist', 'default'] @> array['default', 'artist'] -- True
array['artist', 'default'] @> array['artist', 'event']   -- False

So @> is checks if the right operand is a set-wise subset of the left operand.

I think you're looking for the "overlaps" operator:

&&
overlap (have elements in common)
ARRAY[1,4,3] && ARRAY[2,1] -- True

This operator checks if the set-wise intersection of the left and right operands is non-empty.

Something like:

.whereRaw("tags && '{??}'", [tags])

should server you better.

user_4798630
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