简化CASE缩写

-- With Settings.transformPatternsSimplifyCaseAbbreviation active, this:
SELECT
  a IS NULL OR NVL(a = b, FALSE),
  COALESCE(a = b, a IS NULL),
  COALESCE(a, b) IS NOT DISTINCT FROM b,
  a IS NOT NULL AND NVL(a != b, TRUE),
  COALESCE(a != b, a IS NOT NULL),
  COALESCE(a, b) IS DISTINCT FROM b
FROM tab;

-- ... is transformed into the equivalent expression:
SELECT
  NULLIF(a, b) IS NULL,
  NULLIF(a, b) IS NULL,
  NULLIF(a, b) IS NULL,
  NULLIF(a, b) IS NOT NULL,
  NULLIF(a, b) IS NOT NULL,
  NULLIF(a, b) IS NOT NULL
FROM tab;