CASE到CASE缩写

-- With Settings.transformPatternsCaseToCaseAbbreviation active, this:
SELECT
  CASE WHEN x IS NULL THEN y ELSE x END,
  CASE WHEN x = y THEN NULL ELSE x END,
  CASE WHEN x IS NOT NULL THEN y ELSE z END,
  CASE WHEN x IS NULL THEN y ELSE z END,
  CASE WHEN x = 1 THEN y WHEN x = 2 THEN z END,
FROM tab;

-- ... is transformed into the equivalent expression:
SELECT
  NVL(x, y),
  NULLIF(x, y),
  NVL2(x, y, z),
  NVL2(x, z, y),
  CHOOSE(x, y, z)
FROM tab;

-- With Settings.transformPatternsCaseToCaseAbbreviation active, this:
SELECT
  CASE WHEN x = y THEN TRUE ELSE FALSE END,
  CASE WHEN x = y THEN FALSE ELSE TRUE END,
  CASE x WHEN y THEN TRUE ELSE FALSE END,
  CASE x WHEN y THEN FALSE ELSE TRUE END
FROM tab;

-- ... is transformed into the equivalent expression:
SELECT
  NVL(x = y, FALSE),
  NVL(x <> y, TRUE),
  NVL(x = y, FALSE),
  NVL(x <> y, TRUE)
FROM tab;