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

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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.BinaryPredicate;
import org.apache.impala.analysis.Expr;

/**
 * Normalizes binary predicates of the form <expr> <op> <slot> so that the slot is
 * on the left hand side. Predicates where <slot> is wrapped in a cast (implicit or
 * explicit) are normalized, too. Predicates of the form <constant> <op> <expr>
 * are also normalized so that <constant> is always on the right hand side.
 *
 * Examples:
 * 5 > id -> id < 5
 * cast(0 as double) = id -> id = cast(0 as double)
 * 5 = id + 2 -> id + 2 = 5
 *
 */
public class NormalizeBinaryPredicatesRule implements ExprRewriteRule {
  public static ExprRewriteRule INSTANCE = new NormalizeBinaryPredicatesRule();

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

    if (isExprOpSlotRef(expr) || isConstantOpExpr(expr)) {
      BinaryPredicate.Operator op = ((BinaryPredicate) expr).getOp();
      return new BinaryPredicate(op.converse(), expr.getChild(1), expr.getChild(0));
    }
    return expr;
  }

  boolean isConstantOpExpr(Expr expr) {
    return expr.getChild(0).isConstant() && !expr.getChild(1).isConstant();
  }

  boolean isExprOpSlotRef(Expr expr) {
    return expr.getChild(0).unwrapSlotRef(false) == null
        && expr.getChild(1).unwrapSlotRef(false) != null;
  }
}