PostgreSQL’s New LATERAL Join Type
LATERAL is awesome. It makes a lot of queries that required sub-select joins much simpler to write and later read.It's also great for set returning functions. Even cooler, you don't need to explicitly specify the LATERAL keyword. The query planner will add it for you automatically:    -- NOTE: WITH clause is just to fake a table with data:
    WITH foo AS (
      SELECT 'a' AS name
           , 2 AS quantity
      UNION ALL
      SELECT 'b' AS name
           , 4 AS quantity)
    SELECT t.*
         , x
    FROM foo t
      -- No need to say "LATERAL" here as it's added automatically
      , generate_series(1,quantity) x;
    
    name | quantity | x
    ------+----------+---
    a    |        2 | 1
    a    |        2 | 2
    b    |        4 | 1
    b    |        4 | 2
    b    |        4 | 3
    b    |        4 | 4
    (6 rows)