fe/src/main/java/org/apache/impala/analysis/IsNotEmptyPredicate.java

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package org.apache.impala.analysis;

import org.apache.impala.common.AnalysisException;
import org.apache.impala.thrift.TExprNode;
import org.apache.impala.thrift.TExprNodeType;
import com.google.common.base.Preconditions;

/**
 * Predicate that checks whether a collection is empty or not.
 * This predicate is not user-accessible from SQL, and may be
 * generated as a performance optimization for certain queries.
 * TODO: Pass this Predicate as a TExprNodeType.FUNCTION_CALL
 * to the BE just like the rest of our Predicates. This is not yet
 * done to avoid invasive changes required in FE/BE to deal with
 * resolution of functions with complex-types arguments,
 */
public class IsNotEmptyPredicate extends Predicate {

  public IsNotEmptyPredicate(Expr collectionExpr) {
    super();
    Preconditions.checkNotNull(collectionExpr);
    children_.add(collectionExpr);
  }

  @Override
  protected void analyzeImpl(Analyzer analyzer) throws AnalysisException {
    super.analyzeImpl(analyzer);
    if (!getChild(0).getType().isCollectionType()) {
      throw new AnalysisException("Operand must be a collection type: "
          + getChild(0).toSql() + " is of type " + getChild(0).getType());
    }
    // Avoid influencing cardinality estimates.
    selectivity_ = 1.0;
  }

  @Override
  protected float computeEvalCost() {
    if (!getChild(0).hasCost()) return UNKNOWN_COST;
    return getChild(0).getCost() + IS_NOT_EMPTY_COST;
  }

  @Override
  public String toSqlImpl(ToSqlOptions options) {
    return "!empty(" + getChild(0).toSql(options) + ")";
  }

  @Override
  protected void toThrift(TExprNode msg) {
    msg.node_type = TExprNodeType.IS_NOT_EMPTY_PRED;
  }

  @Override
  public Expr clone() { return new IsNotEmptyPredicate(getChild(0).clone()); }
}