テーブル名と同じカラム名のカラムがあるテーブルに対するPostgresqlとBigQueryの結果の差異

bigquery.sql

WITH a AS ( SELECT 1 AS a, 2 AS b )
SELECT a FROM a ;

-- result::
-- | Row | a.a | a.b |
-- | 1   | 1   | 2   |

-- result (json)::
-- [
--   {
--     "a": {
--       "a": "1",
--       "b": "2"
--     }
--   }
-- ]

postgresql.sql

WITH a AS ( SELECT 1 AS a, 2 AS b )
SELECT a FROM a ;


-- result::
--  a
-- ---
--  1
-- (1 row)

zetasql.sql

-- https://github.com/apstndb/zetasql-sandbox
-- $ echo "WITH a AS ( SELECT 1 AS a, 2 AS b ) SELECT a FROM a ;"| docker run -i --rm zetasql-sandbox analyze-print

WITH
  a AS (
    SELECT
      1 AS a_1,
      2 AS a_2
  )
SELECT
  STRUCT< a INT64, b INT64 > (withrefscan_3.a_1, withrefscan_3.a_2) AS a
FROM
  a AS withrefscan_3;