Array of arrays in PostgreSQL

Question

I\'m using the %% operator on PostgreSQL\'s hstore type which converts a hstore (key-value type effectively) into an array whose elements alternate {{key, value

Answer 1

From a curiosity standpoint, does anyone know why these are not supported?

One generic answer is because arrays are intrinsically anti-relational. Removing repeating values is how you achieve 1st normal form. To have repeating groups of repeating groups seems quite insane from a relational theoretical standpoint.

In general, the relationally-correct thing to do is to extract a table for your repeating values. So if you modeled something like this:

CREATE TABLE users (
  id integer primary key,
  name varchar,
  favorite_colors varchar[],
  ...
);

it would behoove you to redefine this relationally like so:

CREATE TABLE users (
  id integer primary key,
  name varchar,
  ...
);

CREATE TABLE favorite_colors (
  user_id integer references users,
  color varchar
);

Or even:

CREATE TABLE users (
  id integer primary key,
  name varchar,
  ...
);

CREATE TABLE colors (
  color varchar primary key
);

CREATE TABLE favorite_colors (
  user_id integer references users,
  color varchar references colors,
  primary key (user_id, color)
);

Hstore supports a lot of functions, many of which would make it easy to integrate it into a relational worldview. I think the simplest way to solve your problem would be to use the each function to convert your hstore values into relations you can then use like a normal set of values. This is how you address having multiple values in other databases anyway: querying, and working with result sets.