SimplifySelfComparison.java

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

import org.apache.doris.nereids.rules.expression.ExpressionPatternMatcher;
import org.apache.doris.nereids.rules.expression.ExpressionPatternRuleFactory;
import org.apache.doris.nereids.rules.expression.ExpressionRuleType;
import org.apache.doris.nereids.trees.expressions.ComparisonPredicate;
import org.apache.doris.nereids.trees.expressions.EqualTo;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.GreaterThan;
import org.apache.doris.nereids.trees.expressions.GreaterThanEqual;
import org.apache.doris.nereids.trees.expressions.LessThan;
import org.apache.doris.nereids.trees.expressions.LessThanEqual;
import org.apache.doris.nereids.trees.expressions.NullSafeEqual;
import org.apache.doris.nereids.trees.expressions.literal.BooleanLiteral;
import org.apache.doris.nereids.util.ExpressionUtils;

import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * simplify with self comparison
 * such as: a = a --> TRUE
 *          a + b > a + b --> FALSE
 */
public class SimplifySelfComparison implements ExpressionPatternRuleFactory {
    public static SimplifySelfComparison INSTANCE = new SimplifySelfComparison();

    @Override
    public List<ExpressionPatternMatcher<? extends Expression>> buildRules() {
        return ImmutableList.of(
                matchesType(ComparisonPredicate.class)
                        .then(this::rewrite)
                        .toRule(ExpressionRuleType.SIMPLIFY_SELF_COMPARISON)
        );
    }

    private Expression rewrite(ComparisonPredicate comparison) {
        Expression left = comparison.left();
        // expression maybe non-deterministic, but if it's foldable, then it still can simplify self comparison.
        // for example, function `user()`,  `current_timestamp()` are foldable and non-deterministic,
        // then `user() = user()` and `current_timestamp() = current_timestamp()` can simplify to `TRUE`.
        // function `random` is not foldable and non-deterministic,
        // then `random(1, 10) = random(1, 10)` cann't simplify to `TRUE`
        if (!left.containsNonfoldable() && left.equals(comparison.right())) {
            if (comparison instanceof EqualTo
                    || comparison instanceof GreaterThanEqual
                    || comparison instanceof LessThanEqual) {
                return ExpressionUtils.trueOrNull(left);
            }
            if (comparison instanceof NullSafeEqual) {
                return BooleanLiteral.TRUE;
            }
            if (comparison instanceof GreaterThan || comparison instanceof LessThan) {
                return ExpressionUtils.falseOrNull(left);
            }
        }

        return comparison;
    }

}