SimplifyConditionalFunction.java

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//   http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.doris.nereids.rules.expression.rules;

import org.apache.doris.nereids.rules.expression.ExpressionMatchingContext;
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.Expression;
import org.apache.doris.nereids.trees.expressions.functions.scalar.Coalesce;
import org.apache.doris.nereids.trees.expressions.functions.scalar.NullIf;
import org.apache.doris.nereids.trees.expressions.functions.scalar.Nullable;
import org.apache.doris.nereids.trees.expressions.functions.scalar.Nvl;
import org.apache.doris.nereids.trees.expressions.literal.NullLiteral;
import org.apache.doris.nereids.util.TypeCoercionUtils;

import com.google.common.collect.ImmutableList;

import java.util.List;

/**SimplifyConditionalFunction*/
public class SimplifyConditionalFunction implements ExpressionPatternRuleFactory {
    public static SimplifyConditionalFunction INSTANCE = new SimplifyConditionalFunction();

    @Override
    public List<ExpressionPatternMatcher<? extends Expression>> buildRules() {
        return ImmutableList.of(
                matchesType(Coalesce.class).thenApply(SimplifyConditionalFunction::rewriteCoalesce)
                        .toRule(ExpressionRuleType.SIMPLIFY_CONDITIONAL_FUNCTION),
                matchesType(Nvl.class).thenApply(SimplifyConditionalFunction::rewriteNvl)
                        .toRule(ExpressionRuleType.SIMPLIFY_CONDITIONAL_FUNCTION),
                matchesType(NullIf.class).thenApply(SimplifyConditionalFunction::rewriteNullIf)
                        .toRule(ExpressionRuleType.SIMPLIFY_CONDITIONAL_FUNCTION)
        );
    }

    /*
     * coalesce(null, ..., null, expr, null) => expr
     * coalesce(a, null, b, null) => coalesce(a, b)
     * coalesce(a, b_not_nullable, c) => coalesce(a, b_not_nullable)
     * coalesce(expr_not_nullable, ...) => expr_not_nullable
     * coalesce(null, null) => null
     * coalesce(expr) => expr
     * */
    private static Expression rewriteCoalesce(ExpressionMatchingContext<Coalesce> ctx) {
        Coalesce coalesce = ctx.expr;
        ImmutableList.Builder<Expression> childBuilder = ImmutableList.builder();
        for (int i = 0; i < coalesce.arity(); i++) {
            Expression child = coalesce.children().get(i);
            if (child instanceof NullLiteral) {
                continue;
            }
            childBuilder.add(child);
            if (!child.nullable()) {
                break;
            }
        }
        List<Expression> newChildren = childBuilder.build();
        if (newChildren.isEmpty()) {
            return TypeCoercionUtils.ensureSameResultType(
                    coalesce, new NullLiteral(coalesce.getDataType()), ctx.rewriteContext
            );
        } else if (newChildren.size() == 1) {
            return TypeCoercionUtils.ensureSameResultType(
                    coalesce, newChildren.get(0), ctx.rewriteContext
            );
        } else {
            return TypeCoercionUtils.ensureSameResultType(
                    coalesce, coalesce.withChildren(newChildren), ctx.rewriteContext
            );
        }
    }

    /*
    * nvl(null,R) => R
    * nvl(L(not-nullable ),R) => L
    * */
    private static Expression rewriteNvl(ExpressionMatchingContext<Nvl> ctx) {
        Nvl nvl = ctx.expr;
        if (nvl.child(0) instanceof NullLiteral) {
            return TypeCoercionUtils.ensureSameResultType(nvl, nvl.child(1), ctx.rewriteContext);
        }
        if (!nvl.child(0).nullable()) {
            return TypeCoercionUtils.ensureSameResultType(nvl, nvl.child(0), ctx.rewriteContext);
        }
        return nvl;
    }

    /*
    * nullif(null, R) => Null
    * nullif(L, null) => Null
     */
    private static Expression rewriteNullIf(ExpressionMatchingContext<NullIf> ctx) {
        NullIf nullIf = ctx.expr;
        if (nullIf.child(0) instanceof NullLiteral || nullIf.child(1) instanceof NullLiteral) {
            return TypeCoercionUtils.ensureSameResultType(
                    nullIf, new Nullable(nullIf.child(0)), ctx.rewriteContext
            );
        } else {
            return nullIf;
        }
    }
}