NullIfToIf.java

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package org.apache.doris.nereids.rules.expression.rules;

import org.apache.doris.nereids.rules.expression.AbstractExpressionRewriteRule;
import org.apache.doris.nereids.rules.expression.ExpressionRewriteContext;
import org.apache.doris.nereids.trees.expressions.EqualTo;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.functions.scalar.If;
import org.apache.doris.nereids.trees.expressions.functions.scalar.NullIf;
import org.apache.doris.nereids.trees.expressions.literal.NullLiteral;
import org.apache.doris.nereids.util.TypeCoercionUtils;

/**
 * Rewrite nullif(first, second) to if(first = second, null, first).
 */
public class NullIfToIf extends AbstractExpressionRewriteRule {
    public static final NullIfToIf INSTANCE = new NullIfToIf();

    @Override
    public Expression visitNullIf(NullIf nullIf, ExpressionRewriteContext context) {
        NullIf rewritten = (NullIf) super.visitNullIf(nullIf, context);
        return rewrite(rewritten, context);
    }

    public static Expression rewrite(NullIf nullIf, ExpressionRewriteContext context) {
        Expression first = nullIf.left();
        Expression second = nullIf.right();
        If ifExpr = new If(new EqualTo(first, second), new NullLiteral(nullIf.getDataType()), first);
        return TypeCoercionUtils.ensureSameResultType(nullIf, ifExpr, context);
    }
}