-- Combined dataset

WITH

  my_data1 AS (

    SELECT

      'id1' AS src__id,

      'Q1' AS period,

      2 AS Amount_A

  ),

  my_data2 AS (

    SELECT

      'id1' AS src__id,

      'Q1' AS period,

      9 AS Amount_B

    UNION

    SELECT

      'id2' AS src__id,

      'Q2' AS period,

      1 AS Amount_B

  ),

  my_data3 AS (

    SELECT

      'id2' AS src__id,

      'Q2' AS period,

      4 AS Amount_C

  )

SELECT

  COALESCE(my_data1.src__id, my_data2.src__id, my_data3.src__id) AS src__id,

  COALESCE(my_data1.period, my_data2.period, my_data3.period) AS period,

  COALESCE(my_data1.Amount_A, 0) AS Amount_A,

  COALESCE(my_data2.Amount_B, 0) AS Amount_B,

  COALESCE(my_data3.Amount_C, 0) AS Amount_C

FROM

  my_data1

FULL JOIN my_data2 ON my_data1.src__id = my_data2.src__id AND my_data1.period = my_data2.period

FULL JOIN my_data3 ON my_data1.src__id = my_data3.src__id AND my_data1.period = my_data3.period

​