-- Table1:
        column_name        |          data_type
---------------------------+-----------------------------
 id                        | integer
 name                      | text
 account_id                | integer
 tags                      | ARRAY {tag1,tag_2,'tag 3',...}

-- Table2:
        column_name        |          data_type
---------------------------+-----------------------------
 id                        | integer
 name                      | text
 account_id                | integer
 tags                      | ARRAY {tag1,tag_2,'tag 3',...}

-- Tags:
        column_name        |          data_type
---------------------------+-----------------------------
 id                        | integer
 name                      | text
 account_id                | integer
 source                    | enum (either 'table1' or 'table2')

CREATE table tags
    AS
    SELECT
      DISTINCT(UNNEST(table1.tags)) AS name,
      table1.account_id AS account_id,
      'table1' as source FROM table1
    UNION
    SELECT
      DISTINCT(UNNEST(table2.tags)) AS name,
      table2.account_id AS account_id,
      'table2' as source FROM table2;
ALTER TABLE tags ADD COLUMN id SERIAL PRIMARY KEY;