How to use

NullIfExpression

in

com.facebook.presto.sql.tree

@Override
protected Object visitNullIfExpression(NullIfExpression node, Object context)
  Object first = process(node.getFirst(), context);
  if (first == null) {
    return null;
  Object second = process(node.getSecond(), context);
  if (second == null) {
    return first;
  Type firstType = type(node.getFirst());
  Type secondType = type(node.getSecond());
    return new NullIfExpression(toExpression(first, firstType), toExpression(second, secondType));

@Override
protected R visitNullIfExpression(NullIfExpression node, C context)
{
  process(node.getFirst(), context);
  process(node.getSecond(), context);
  return null;
}

check(!filter.isPresent(), "FILTER not valid for 'nullif' function", context);
return new NullIfExpression(
    getLocation(context),
    (Expression) visit(context.expression(0)),

@Override
protected String visitNullIfExpression(NullIfExpression node, Void context)
{
  return "NULLIF(" + process(node.getFirst(), context) + ", " + process(node.getSecond(), context) + ')';
}

@Test
public void testNullIf()
{
  assertExpression("nullif(42, 87)", new NullIfExpression(new LongLiteral("42"), new LongLiteral("87")));
  assertExpression("nullif(42, null)", new NullIfExpression(new LongLiteral("42"), new NullLiteral()));
  assertExpression("nullif(null, null)", new NullIfExpression(new NullLiteral(), new NullLiteral()));
  assertInvalidExpression("nullif(1)", "Invalid number of arguments for 'nullif' function");
  assertInvalidExpression("nullif(1, 2, 3)", "Invalid number of arguments for 'nullif' function");
  assertInvalidExpression("nullif(42, 87) filter (where true)", "FILTER not valid for 'nullif' function");
  assertInvalidExpression("nullif(42, 87) OVER ()", "OVER clause not valid for 'nullif' function");
}

@Override
protected Boolean visitNullIfExpression(NullIfExpression node, Void context)
{
  return process(node.getFirst(), context) && process(node.getSecond(), context);
}

@Override
protected Object visitNullIfExpression(NullIfExpression node, Object context)
  Object first = process(node.getFirst(), context);
  if (first == null) {
    return null;
  Object second = process(node.getSecond(), context);
  if (second == null) {
    return first;
  Type firstType = expressionTypes.get(node.getFirst());
  Type secondType = expressionTypes.get(node.getSecond());
    return new NullIfExpression(toExpression(first, firstType), toExpression(second, secondType));

@Test
public void testExpressionsThatMayReturnNullOnNonNullInput()
{
  List<Expression> candidates = ImmutableList.of(
      new Cast(nameReference("b"), "BIGINT", true), // try_cast
      new FunctionCall(QualifiedName.of("try"), ImmutableList.of(nameReference("b"))),
      new NullIfExpression(nameReference("b"), number(1)),
      new IfExpression(nameReference("b"), number(1), new NullLiteral()),
      new DereferenceExpression(nameReference("b"), identifier("x")),
      new InPredicate(nameReference("b"), new InListExpression(ImmutableList.of(new NullLiteral()))),
      new SearchedCaseExpression(ImmutableList.of(new WhenClause(new IsNotNullPredicate(nameReference("b")), new NullLiteral())), Optional.empty()),
      new SimpleCaseExpression(nameReference("b"), ImmutableList.of(new WhenClause(number(1), new NullLiteral())), Optional.empty()),
      new SubscriptExpression(new ArrayConstructor(ImmutableList.of(new NullLiteral())), nameReference("b")));
  for (Expression candidate : candidates) {
    EqualityInference.Builder builder = new EqualityInference.Builder();
    builder.extractInferenceCandidates(equals(nameReference("b"), nameReference("x")));
    builder.extractInferenceCandidates(equals(nameReference("a"), candidate));
    EqualityInference inference = builder.build();
    List<Expression> equalities = inference.generateEqualitiesPartitionedBy(matchesSymbols("b")).getScopeStraddlingEqualities();
    assertEquals(equalities.size(), 1);
    assertTrue(equalities.get(0).equals(equals(nameReference("x"), nameReference("b"))) || equalities.get(0).equals(equals(nameReference("b"), nameReference("x"))));
  }
}

@Override
protected Type visitNullIfExpression(NullIfExpression node, StackableAstVisitorContext<Context> context)
{
  Type firstType = process(node.getFirst(), context);
  Type secondType = process(node.getSecond(), context);
  if (!typeManager.getCommonSuperType(firstType, secondType).isPresent()) {
    throw new SemanticException(TYPE_MISMATCH, node, "Types are not comparable with NULLIF: %s vs %s", firstType, secondType);
  }
  return setExpressionType(node, firstType);
}

check(!filter.isPresent(), "FILTER not valid for 'nullif' function", context);
return new NullIfExpression(
    getLocation(context),
    (Expression) visit(context.expression(0)),

@Override
protected RowExpression visitNullIfExpression(NullIfExpression node, Void context)
{
  RowExpression first = process(node.getFirst(), context);
  RowExpression second = process(node.getSecond(), context);
  return call(
      nullIfSignature(getType(node), first.getType(), second.getType()),
      getType(node),
      first,
      second);
}

@Test
public void testNullIf()
{
  assertExpression("nullif(42, 87)", new NullIfExpression(new LongLiteral("42"), new LongLiteral("87")));
  assertExpression("nullif(42, null)", new NullIfExpression(new LongLiteral("42"), new NullLiteral()));
  assertExpression("nullif(null, null)", new NullIfExpression(new NullLiteral(), new NullLiteral()));
  assertInvalidExpression("nullif(1)", "Invalid number of arguments for 'nullif' function");
  assertInvalidExpression("nullif(1, 2, 3)", "Invalid number of arguments for 'nullif' function");
  assertInvalidExpression("nullif(42, 87) filter (where true)", "FILTER not valid for 'nullif' function");
  assertInvalidExpression("nullif(42, 87) OVER ()", "OVER clause not valid for 'nullif' function");
}

@Override
protected String visitNullIfExpression(NullIfExpression node, Void context) {
  return "NULLIF(" + process(node.getFirst(), context) + ", " + process(node.getSecond(), context) + ')';
}

check(!distinct, "DISTINCT not valid for 'nullif' function", context);
return new NullIfExpression(
    getLocation(context),
    (Expression) visit(context.expression(0)),

@Override
protected String visitNullIfExpression(NullIfExpression node, Boolean unmangleNames)
{
  return "NULLIF(" + process(node.getFirst(), unmangleNames) + ", " + process(node.getSecond(), unmangleNames) + ')';
}

@Override
protected Boolean visitNullIfExpression(NullIfExpression node, Void context)
{
  return process(node.getFirst(), context) && process(node.getSecond(), context);
}

@Override
protected String visitNullIfExpression(NullIfExpression node, Void context)
{
  return "NULLIF(" + process(node.getFirst(), context) + ", " + process(node.getSecond(), context) + ')';
}

@Override
protected R visitNullIfExpression(NullIfExpression node, C context)
{
  process(node.getFirst(), context);
  process(node.getSecond(), context);
  return null;
}

@Override
protected String visitNullIfExpression(NullIfExpression node, Boolean unmangleNames)
{
  return "NULLIF(" + process(node.getFirst(), unmangleNames) + ", " + process(node.getSecond(), unmangleNames) + ')';
}

@Override
protected R visitNullIfExpression(NullIfExpression node, C context)
{
  process(node.getFirst(), context);
  process(node.getSecond(), context);
  return null;
}