fe/src/main/java/org/apache/impala/rewrite/NormalizeExprsRule.java

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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package org.apache.impala.rewrite;

import org.apache.impala.analysis.Analyzer;
import org.apache.impala.analysis.BoolLiteral;
import org.apache.impala.analysis.CompoundPredicate;
import org.apache.impala.analysis.Expr;

/**
 * Normalizes CompoundPredicates by ensuring that if either child of AND or OR is a
 * BoolLiteral, then the left (i.e. first) child is a BoolLiteral.
 *
 * Examples:
 * id = 0 && true -> true && id = 0
 */
public class NormalizeExprsRule implements ExprRewriteRule {
  public static ExprRewriteRule INSTANCE = new NormalizeExprsRule();

  @Override
  public Expr apply(Expr expr, Analyzer analyzer) {
    if (!expr.isAnalyzed()) return expr;

    // TODO: add normalization for other expr types.
    if (expr instanceof CompoundPredicate) {
      return normalizeCompoundPredicate((CompoundPredicate) expr);
    }
    return expr;
  }

  private Expr normalizeCompoundPredicate(CompoundPredicate expr) {
    if (expr.getOp() == CompoundPredicate.Operator.NOT) return expr;

    if (!(expr.getChild(0) instanceof BoolLiteral)
        && expr.getChild(1) instanceof BoolLiteral) {
      return new CompoundPredicate(expr.getOp(), expr.getChild(1), expr.getChild(0));
    }
    return expr;
  }
}