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// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package org.apache.impala.analysis;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;

import org.apache.impala.analysis.Path.PathType;
import org.apache.impala.authorization.Privilege;
import org.apache.impala.catalog.Column;
import org.apache.impala.catalog.FeTable;
import org.apache.impala.catalog.FeView;
import org.apache.impala.catalog.StructField;
import org.apache.impala.catalog.StructType;
import org.apache.impala.catalog.TableLoadingException;
import org.apache.impala.common.AnalysisException;
import org.apache.impala.common.ColumnAliasGenerator;
import org.apache.impala.common.TableAliasGenerator;
import org.apache.impala.common.TreeNode;
import org.apache.impala.rewrite.ExprRewriter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Preconditions;
import com.google.common.base.Predicates;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;

/**
 * Representation of a single select block, including GROUP BY, ORDER BY and HAVING
 * clauses.
 */
public class SelectStmt extends QueryStmt {
  private final static Logger LOG = LoggerFactory.getLogger(SelectStmt.class);

  /**
   * Impala 3.x and earlier provide non-standard support for a single ordinal
   * in the HAVING clause:
   *
   * SELECT region, count(*), count(*) > 10 FROM sales
   * HAVING 3
   *
   * Most other SQL dialects do not allow ordinals in expressions (such as
   * HAVING), only in lists (GROUP BY, ORDER BY). The standard way to express
   * the above is:
   *
   * SELECT region, count(*) FROM sales
   * HAVING count(*) > 10
   *
   * Or, better (not currently supported by IMPALA):
   *
   * SELECT region, count(*) c FROM SALES
   * HAVING c > 10
   *
   * We intend to disable this non-standard feature in the next major
   * release. For now, we leave the feature/bug enabled, controlled by
   * the following constant.
   *
   * In that same release, we will enable the third example above.
   * At present, all that is supported is the odd:
   *
   * SELECT region, count(*), count(*) > 10 p FROM sales
   * HAVING p
   *
   * See IMPALA-7844.
   */
  public static final boolean ALLOW_ORDINALS_IN_HAVING = true;

  /////////////////////////////////////////
  // BEGIN: Members that need to be reset()

  protected SelectList selectList_;
  protected final List<String> colLabels_; // lower case column labels
  protected final FromClause fromClause_;
  protected Expr whereClause_;
  protected List<Expr> groupingExprs_;
  protected Expr havingClause_;  // original having clause

  // havingClause with aliases and agg output resolved
  private Expr havingPred_;

  // set if we have any kind of aggregation operation, include SELECT DISTINCT
  private MultiAggregateInfo multiAggInfo_;

  // set if we have AnalyticExprs in the select list/order by clause
  private AnalyticInfo analyticInfo_;

  // substitutes all exprs in this select block to reference base tables
  // directly
  private ExprSubstitutionMap baseTblSmap_ = new ExprSubstitutionMap();

  // END: Members that need to be reset()
  /////////////////////////////////////////

  // SQL string of this SelectStmt before inline-view expression substitution.
  // Set in analyze().
  protected String sqlString_;

  SelectStmt(SelectList selectList,
             FromClause fromClause,
             Expr wherePredicate, List<Expr> groupingExprs,
             Expr havingPredicate, List<OrderByElement> orderByElements,
             LimitElement limitElement) {
    super(orderByElements, limitElement);
    selectList_ = selectList;
    if (fromClause == null) {
      fromClause_ = new FromClause();
    } else {
      fromClause_ = fromClause;
    }
    whereClause_ = wherePredicate;
    groupingExprs_ = groupingExprs;
    havingClause_ = havingPredicate;
    colLabels_ = new ArrayList<>();
    havingPred_ = null;
    multiAggInfo_ = null;
    sortInfo_ = null;
  }

  /**
   * @return the original select list items from the query
   */
  public SelectList getSelectList() { return selectList_; }

  /**
   * @return the HAVING clause post-analysis and with aliases resolved
   */
  public Expr getHavingPred() { return havingPred_; }

  @Override
  public List<String> getColLabels() { return colLabels_; }

  public List<TableRef> getTableRefs() { return fromClause_.getTableRefs(); }
  public boolean hasWhereClause() { return whereClause_ != null; }
  public boolean hasGroupByClause() { return groupingExprs_ != null; }
  public Expr getWhereClause() { return whereClause_; }
  public void setWhereClause(Expr whereClause) { whereClause_ = whereClause; }
  public MultiAggregateInfo getMultiAggInfo() { return multiAggInfo_; }
  public boolean hasMultiAggInfo() { return multiAggInfo_ != null; }
  public AnalyticInfo getAnalyticInfo() { return analyticInfo_; }
  public boolean hasAnalyticInfo() { return analyticInfo_ != null; }
  public boolean hasHavingClause() { return havingClause_ != null; }
  public ExprSubstitutionMap getBaseTblSmap() { return baseTblSmap_; }

  // Column alias generator used during query rewriting.
  private ColumnAliasGenerator columnAliasGenerator_ = null;
  public ColumnAliasGenerator getColumnAliasGenerator() {
    if (columnAliasGenerator_ == null) {
      columnAliasGenerator_ = new ColumnAliasGenerator(colLabels_, null);
    }
    return columnAliasGenerator_;
  }

  // Table alias generator used during query rewriting.
  private TableAliasGenerator tableAliasGenerator_ = null;
  public TableAliasGenerator getTableAliasGenerator() {
    if (tableAliasGenerator_ == null) {
      tableAliasGenerator_ = new TableAliasGenerator(analyzer_, null);
    }
    return tableAliasGenerator_;
  }

  @Override
  public void setDoTableMasking(boolean doTableMasking) {
    fromClause_.setDoTableMasking(doTableMasking);
  }

  /**
   * Creates resultExprs and baseTblResultExprs.
   */
  @Override
  public void analyze(Analyzer analyzer) throws AnalysisException {
    if (isAnalyzed()) return;
    super.analyze(analyzer);
    new SelectAnalyzer(analyzer).analyze();
  }

  /**
   * Algorithm class for the SELECT statement analyzer. Holds
   * the analyzer and intermediate state.
   */
  private class SelectAnalyzer {

    private final Analyzer analyzer_;
    private List<Expr> groupingExprsCopy_;
    private List<FunctionCallExpr> aggExprs_;
    private ExprSubstitutionMap ndvSmap_;
    private ExprSubstitutionMap countAllMap_;

    private SelectAnalyzer(Analyzer analyzer) {
      this.analyzer_ = analyzer;
    }

    private void analyze() throws AnalysisException {
      // Start out with table refs to establish aliases.
      fromClause_.analyze(analyzer_);

      analyzeSelectClause();
      verifyResultExprs();
      registerViewColumnPrivileges();
      analyzeWhereClause();
      createSortInfo(analyzer_);

      // Analyze aggregation-relevant components of the select block (Group By
      // clause, select list, Order By clause), substitute AVG with SUM/COUNT,
      // create the AggregationInfo, including the agg output tuple, and transform
      // all post-agg exprs given AggregationInfo's smap.
      analyzeHavingClause();
      if (checkForAggregates()) {
        verifyAggSemantics();
        analyzeGroupingExprs();
        collectAggExprs();
        rewriteCountDistinct();
        buildAggregateExprs();
        buildResultExprs();
        verifyAggregation();
      }

      createAnalyticInfo();
      if (evaluateOrderBy_) createSortTupleInfo(analyzer_);

      // Remember the SQL string before inline-view expression substitution.
      sqlString_ = toSql();
      if (origSqlString_ == null) origSqlString_ = sqlString_;
      resolveInlineViewRefs();

      // If this block's select-project-join portion returns an empty result set and the
      // block has no aggregation, then mark this block as returning an empty result set.
      if (analyzer_.hasEmptySpjResultSet() && multiAggInfo_ == null) {
        analyzer_.setHasEmptyResultSet();
      }

      buildColumnLineageGraph();
    }

    private void analyzeSelectClause() throws AnalysisException {
      // Generate !empty() predicates to filter out empty collections.
      // Skip this step when analyzing a WITH-clause because CollectionTableRefs
      // do not register collection slots in their parent in that context
      // (see CollectionTableRef.analyze()).
      if (!analyzer_.hasWithClause()) registerIsNotEmptyPredicates();

      // analyze plan hints from select list
      selectList_.analyzePlanHints(analyzer_);

      // populate resultExprs_, aliasSmap_, and colLabels_
      for (int i = 0; i < selectList_.getItems().size(); ++i) {
        SelectListItem item = selectList_.getItems().get(i);
        if (item.isStar()) {
          if (item.getRawPath() != null) {
            Path resolvedPath = analyzeStarPath(item.getRawPath(), analyzer_);
            expandStar(resolvedPath);
          } else {
            expandStar();
          }
        } else {
          // Analyze the resultExpr before generating a label to ensure enforcement
          // of expr child and depth limits (toColumn() label may call toSql()).
          item.getExpr().analyze(analyzer_);
          if (item.getExpr().contains(Predicates.instanceOf(Subquery.class))) {
            throw new AnalysisException(
                "Subqueries are not supported in the select list.");
          }
          resultExprs_.add(item.getExpr());
          String label = item.toColumnLabel(i, analyzer_.useHiveColLabels());
          SlotRef aliasRef = new SlotRef(label);
          Expr existingAliasExpr = aliasSmap_.get(aliasRef);
          if (existingAliasExpr != null && !existingAliasExpr.equals(item.getExpr())) {
            // If we have already seen this alias, it refers to more than one column and
            // therefore is ambiguous.
            ambiguousAliasList_.add(aliasRef);
          }
          aliasSmap_.put(aliasRef, item.getExpr().clone());
          colLabels_.add(label);
        }
      }
    }

    private void verifyResultExprs() throws AnalysisException {
      // Star exprs only expand to the scalar-typed columns/fields, so
      // the resultExprs_ could be empty.
      if (resultExprs_.isEmpty()) {
        throw new AnalysisException("The star exprs expanded to an empty select list " +
            "because the referenced tables only have complex-typed columns.\n" +
            "Star exprs only expand to scalar-typed columns because " +
            "complex-typed exprs " +
            "are currently not supported in the select list.\n" +
            "Affected select statement:\n" + toSql());
      }

      for (Expr expr: resultExprs_) {
        // Complex types are currently not supported in the select list because
        // we'd need to serialize them in a meaningful way.
        if (expr.getType().isComplexType()) {
          throw new AnalysisException(String.format(
              "Expr '%s' in select list returns a complex type '%s'.\n" +
              "Only scalar types are allowed in the select list.",
              expr.toSql(), expr.getType().toSql()));
        }
        if (!expr.getType().isSupported()) {
          throw new AnalysisException("Unsupported type '"
              + expr.getType().toSql() + "' in '" + expr.toSql() + "'.");
        }
      }

      if (TreeNode.contains(resultExprs_, AnalyticExpr.class)) {
        if (fromClause_.isEmpty()) {
          throw new AnalysisException("Analytic expressions require FROM clause.");
        }

        // do this here, not after analyzeAggregation(), otherwise the AnalyticExprs
        // will get substituted away
        if (selectList_.isDistinct()) {
          throw new AnalysisException(
              "cannot combine SELECT DISTINCT with analytic functions");
        }
      }
    }

    private void analyzeWhereClause() throws AnalysisException {
      if (whereClause_ == null) return;
      whereClause_.analyze(analyzer_);
      if (whereClause_.contains(Expr.IS_AGGREGATE)) {
        throw new AnalysisException(
            "aggregate function not allowed in WHERE clause");
      }
      whereClause_.checkReturnsBool("WHERE clause", false);
      Expr e = whereClause_.findFirstOf(AnalyticExpr.class);
      if (e != null) {
        throw new AnalysisException(
            "WHERE clause must not contain analytic expressions: " + e.toSql());
      }
      analyzer_.registerConjuncts(whereClause_, false);
    }

    /**
     * Generates and registers !empty() predicates to filter out empty
     * collections directly in the parent scan of collection table refs. This is
     * a performance optimization to avoid the expensive processing of empty
     * collections inside a subplan that would yield an empty result set.
     *
     * For correctness purposes, the predicates are generated in cases where we
     * can ensure that they will be assigned only to the parent scan, and no other
     * plan node.
     *
     * The conditions are as follows:
     * - collection table ref is relative and non-correlated
     * - collection table ref represents the rhs of an inner/cross/semi join
     * - collection table ref's parent tuple is not outer joined
     *
     * Example: table T has field A which is of type array<array<int>>.
     * 1) ... T join T.A a join a.item a_nest ... :
     *                       all nodes on the path T -> a -> a_nest
     *                       are required so are checked for !empty.
     * 2) ... T left outer join T.A a join a.item a_nest ... : no !empty.
     * 3) ... T join T.A a left outer join a.item a_nest ... :
     *                       a checked for !empty.
     * 4) ... T left outer join T.A a left outer join a.item a_nest ... :
     *                       no !empty.
     *
     *
     * TODO: In some cases, it is possible to generate !empty() predicates for
     * a correlated table ref, but in general, that is not correct for non-trivial
     * query blocks. For example, if the block with the correlated ref has an
     * aggregation then adding a !empty() predicate would incorrectly discard rows
     * from the final result set.
     *
     * TODO: Evaluating !empty() predicates at non-scan nodes interacts poorly with
     * our BE projection of collection slots. For example, rows could incorrectly
     * be filtered if a !empty() predicate is assigned to a plan node that comes
     * after the unnest of the collection that also performs the projection.
     */
    private void registerIsNotEmptyPredicates() throws AnalysisException {
      for (TableRef tblRef: fromClause_.getTableRefs()) {
        Preconditions.checkState(tblRef.isResolved());
        if (!(tblRef instanceof CollectionTableRef)) continue;
        CollectionTableRef ref = (CollectionTableRef) tblRef;
        // Skip non-relative and correlated refs.
        if (!ref.isRelative() || ref.isCorrelated()) continue;
        // Skip outer and anti joins.
        if (ref.getJoinOp().isOuterJoin() || ref.getJoinOp().isAntiJoin()) continue;
        // Do not generate a predicate if the parent tuple is outer joined.
        if (analyzer_.isOuterJoined(ref.getResolvedPath().getRootDesc().getId()))
          continue;
        IsNotEmptyPredicate isNotEmptyPred =
            new IsNotEmptyPredicate(ref.getCollectionExpr().clone());
        isNotEmptyPred.analyze(analyzer_);
        // Register the predicate as an On-clause conjunct because it should only
        // affect the result of this join and not the whole FROM clause.
        analyzer_.registerOnClauseConjuncts(
            Lists.<Expr>newArrayList(isNotEmptyPred), ref);
      }
    }

    /**
      * Populates baseTblSmap_ with our combined inline view smap and creates
      * baseTblResultExprs.
      */
    private void resolveInlineViewRefs()
        throws AnalysisException {
      // Gather the inline view substitution maps from the enclosed inline views
      for (TableRef tblRef: fromClause_) {
        if (tblRef instanceof InlineViewRef) {
          InlineViewRef inlineViewRef = (InlineViewRef) tblRef;
          baseTblSmap_ =
              ExprSubstitutionMap.combine(baseTblSmap_, inlineViewRef.getBaseTblSmap());
        }
      }
      baseTblResultExprs_ =
          Expr.trySubstituteList(resultExprs_, baseTblSmap_, analyzer_, false);
      if (LOG.isTraceEnabled()) {
        LOG.trace("baseTblSmap_: " + baseTblSmap_.debugString());
        LOG.trace("resultExprs: " + Expr.debugString(resultExprs_));
        LOG.trace("baseTblResultExprs: " + Expr.debugString(baseTblResultExprs_));
      }
    }

    /**
     * Resolves the given raw path as a STAR path and checks its legality.
     * Returns the resolved legal path, or throws if the raw path could not
     * be resolved or is an illegal star path.
     */
    private Path analyzeStarPath(List<String> rawPath, Analyzer analyzer)
        throws AnalysisException {
      Path resolvedPath = null;
      try {
        resolvedPath = analyzer.resolvePath(rawPath, PathType.STAR);
      } catch (TableLoadingException e) {
        // Should never happen because we only check registered table aliases.
        Preconditions.checkState(false);
      }
      Preconditions.checkNotNull(resolvedPath);
      return resolvedPath;
    }

    /**
     * Expand "*" select list item, ignoring semi-joined tables as well as
     * complex-typed fields because those are currently illegal in any select
     * list (even for inline views, etc.)
     */
    private void expandStar() throws AnalysisException {
      if (fromClause_.isEmpty()) {
        throw new AnalysisException(
            "'*' expression in select list requires FROM clause.");
      }
      // expand in From clause order
      for (TableRef tableRef: fromClause_) {
        if (analyzer_.isSemiJoined(tableRef.getId())) continue;
        Path resolvedPath = new Path(tableRef.getDesc(),
            Collections.<String>emptyList());
        Preconditions.checkState(resolvedPath.resolve());
        expandStar(resolvedPath);
      }
    }

    /**
     * Expand "path.*" from a resolved path, ignoring complex-typed fields
     * because those are currently illegal in any select list (even for
     * inline views, etc.)
     */
    private void expandStar(Path resolvedPath)
        throws AnalysisException {
      Preconditions.checkState(resolvedPath.isResolved());
      if (resolvedPath.destTupleDesc() != null &&
          resolvedPath.destTupleDesc().getTable() != null &&
          resolvedPath.destTupleDesc().getPath().getMatchedTypes().isEmpty()) {
        // The resolved path targets a registered tuple descriptor of a catalog
        // table. Expand the '*' based on the Hive-column order.
        TupleDescriptor tupleDesc = resolvedPath.destTupleDesc();
        FeTable table = tupleDesc.getTable();
        for (Column c: table.getColumnsInHiveOrder()) {
          addStarResultExpr(resolvedPath, c.getName());
        }
      } else {
        // The resolved path does not target the descriptor of a catalog table.
        // Expand '*' based on the destination type of the resolved path.
        Preconditions.checkState(resolvedPath.destType().isStructType());
        StructType structType = (StructType) resolvedPath.destType();
        Preconditions.checkNotNull(structType);

        // Star expansion for references to nested collections.
        // Collection Type                    Star Expansion
        // array<int>                     --> item
        // array<struct<f1,f2,...,fn>>    --> f1, f2, ..., fn
        // map<int,int>                   --> key, value
        // map<int,struct<f1,f2,...,fn>>  --> key, f1, f2, ..., fn
        if (structType instanceof CollectionStructType) {
          CollectionStructType cst = (CollectionStructType) structType;
          if (cst.isMapStruct()) {
            addStarResultExpr(resolvedPath, Path.MAP_KEY_FIELD_NAME);
          }
          if (cst.getOptionalField().getType().isStructType()) {
            structType = (StructType) cst.getOptionalField().getType();
            for (StructField f: structType.getFields()) {
              addStarResultExpr(
                  resolvedPath, cst.getOptionalField().getName(), f.getName());
            }
          } else if (cst.isMapStruct()) {
            addStarResultExpr(resolvedPath, Path.MAP_VALUE_FIELD_NAME);
          } else {
            addStarResultExpr(resolvedPath, Path.ARRAY_ITEM_FIELD_NAME);
          }
        } else {
          // Default star expansion.
          for (StructField f: structType.getFields()) {
            addStarResultExpr(resolvedPath, f.getName());
          }
        }
      }
    }

    /**
     * Helper function used during star expansion to add a single result expr
     * based on a given raw path to be resolved relative to an existing path.
     * Ignores paths with a complex-typed destination because they are currently
     * illegal in any select list (even for inline views, etc.)
     */
    private void addStarResultExpr(Path resolvedPath,
        String... relRawPath) throws AnalysisException {
      Path p = Path.createRelPath(resolvedPath, relRawPath);
      Preconditions.checkState(p.resolve());
      if (p.destType().isComplexType()) return;
      SlotDescriptor slotDesc = analyzer_.registerSlotRef(p);
      SlotRef slotRef = new SlotRef(slotDesc);
      slotRef.analyze(analyzer_);
      resultExprs_.add(slotRef);
      colLabels_.add(relRawPath[relRawPath.length - 1]);
    }

    /**
     * Registers view column privileges only when the view a catalog view.
     */
    private void registerViewColumnPrivileges() {
      for (TableRef tableRef: fromClause_.getTableRefs()) {
        if (!(tableRef instanceof InlineViewRef)) continue;
        InlineViewRef inlineViewRef = (InlineViewRef) tableRef;
        FeView view = inlineViewRef.getView();
        // For, local views (CTE), the view definition is explicitly defined in the query,
        // this requires registering base column privileges instead of view column
        // privileges. For example:
        //
        // with v as (select id as foo from functional.alltypes) select foo from v
        //
        // The query will register "functional.alltypes.id" column instead of
        // "v.foo" column. This behavior is similar to inline views, e.g.
        //
        // select foo from (select id as foo from functional.alltypes) v
        //
        // The query will register "functional.alltypes.id" column instead of "v.foo"
        // column.
        //
        // Contrasting this with catalog views.
        //
        // create view v(foo) as select id from functional.alltypes
        // select v.foo from v
        //
        // The "select v.foo from v" query requires "v.foo" view column privilege because
        // the "v" view definition is not exposed in the query. This behavior is also
        // consistent with view access, such that the query requires a "select" privilege
        // on "v" view and not "functional.alltypes" table.
        boolean isCatalogView = view != null && !view.isLocalView();
        if (!isCatalogView) continue;
        for (Expr expr: getResultExprs()) {
          List<Expr> slotRefs = new ArrayList<>();
          expr.collectAll(Predicates.instanceOf(SlotRef.class), slotRefs);
          for (Expr e: slotRefs) {
            SlotRef slotRef = (SlotRef) e;
            analyzer_.registerPrivReq(builder -> builder
                .allOf(Privilege.SELECT)
                .onColumn(view.getDb().getName(), view.getName(),
                    slotRef.getDesc().getLabel(), view.getOwnerUser())
                .build());
          }
        }
      }
    }

    /**
     * Analyze the HAVING clause. The HAVING clause is a predicate, not a list
     * (like GROUP BY or ORDER BY) and so cannot contain ordinals.
     *
     * At present, Impala's alias substitution logic only works for top-level
     * expressions in a list. Since HAVING is a predicate, alias substitution
     * does not work (the top-level predicate in HAVING is a Boolean expression.)
     *
     * TODO: Modify alias substitution to work like column resolution so that aliases
     * can appear anywhere in the expression. Then, enable alias substitution in HAVING.
     */
    private void analyzeHavingClause() throws AnalysisException {
      // Analyze the HAVING clause first so we can check if it contains aggregates.
      // We need to analyze/register it even if we are not computing aggregates.
      if (havingClause_ == null) return;
      // can't contain subqueries
      if (havingClause_.contains(Predicates.instanceOf(Subquery.class))) {
        throw new AnalysisException(
            "Subqueries are not supported in the HAVING clause.");
      }
      // Resolve (top-level) aliases and analyzes
      havingPred_ = resolveReferenceExpr(havingClause_, "HAVING", analyzer_,
          ALLOW_ORDINALS_IN_HAVING);
      // can't contain analytic exprs
      Expr analyticExpr = havingPred_.findFirstOf(AnalyticExpr.class);
      if (analyticExpr != null) {
        throw new AnalysisException(
            "HAVING clause must not contain analytic expressions: "
               + analyticExpr.toSql());
      }
      havingPred_.checkReturnsBool("HAVING clause", true);
    }

    private boolean checkForAggregates() throws AnalysisException {
      if (groupingExprs_ == null && !selectList_.isDistinct()
          && !TreeNode.contains(resultExprs_, Expr.IS_AGGREGATE)
          && (havingPred_ == null
              || !havingPred_.contains(Expr.IS_AGGREGATE))
          && (sortInfo_ == null
              || !TreeNode.contains(sortInfo_.getSortExprs(),
                                    Expr.IS_AGGREGATE))) {
        // We're not computing aggregates but we still need to register the HAVING
        // clause which could, e.g., contain a constant expression evaluating to false.
        if (havingPred_ != null) analyzer_.registerConjuncts(havingPred_, true);
        return false;
      }
      return true;
    }

    private void verifyAggSemantics() throws AnalysisException {
      // If we're computing an aggregate, we must have a FROM clause.
      if (fromClause_.isEmpty()) {
        throw new AnalysisException(
            "aggregation without a FROM clause is not allowed");
      }

      if (selectList_.isDistinct()
          && (groupingExprs_ != null
              || TreeNode.contains(resultExprs_, Expr.IS_AGGREGATE)
              || (havingPred_ != null
                  && havingPred_.contains(Expr.IS_AGGREGATE)))) {
        throw new AnalysisException(
          "cannot combine SELECT DISTINCT with aggregate functions or GROUP BY");
      }

      // Disallow '*' with explicit GROUP BY or aggregation function (we can't group by
      // '*', and if you need to name all star-expanded cols in the group by clause you
      // might as well do it in the select list).
      if (groupingExprs_ != null ||
          TreeNode.contains(resultExprs_, Expr.IS_AGGREGATE)) {
        for (SelectListItem item : selectList_.getItems()) {
          if (item.isStar()) {
            throw new AnalysisException(
                "cannot combine '*' in select list with grouping or aggregation");
          }
        }
      }

      // disallow subqueries in the GROUP BY clause
      if (groupingExprs_ != null) {
        for (Expr expr: groupingExprs_) {
          if (expr.contains(Predicates.instanceOf(Subquery.class))) {
            throw new AnalysisException(
                "Subqueries are not supported in the GROUP BY clause.");
          }
        }
      }
    }

    private void analyzeGroupingExprs() throws AnalysisException {
      if (groupingExprs_ == null) {
        groupingExprsCopy_ = new ArrayList<>();
        return;
      }
      // make a deep copy here, we don't want to modify the original
      // exprs during analysis (in case we need to print them later)
      groupingExprsCopy_ = Expr.cloneList(groupingExprs_);
      substituteOrdinalsAndAliases(groupingExprsCopy_, "GROUP BY", analyzer_);

      for (int i = 0; i < groupingExprsCopy_.size(); ++i) {
        groupingExprsCopy_.get(i).analyze(analyzer_);
        if (groupingExprsCopy_.get(i).contains(Expr.IS_AGGREGATE)) {
          // reference the original expr in the error msg
          throw new AnalysisException(
              "GROUP BY expression must not contain aggregate functions: "
                  + groupingExprs_.get(i).toSql());
        }
        if (groupingExprsCopy_.get(i).contains(AnalyticExpr.class)) {
          // reference the original expr in the error msg
          throw new AnalysisException(
              "GROUP BY expression must not contain analytic expressions: "
                  + groupingExprsCopy_.get(i).toSql());
        }
      }
    }

    private void collectAggExprs() {
      // Collect the aggregate expressions from the SELECT, HAVING and ORDER BY clauses
      // of this statement.
      aggExprs_ = new ArrayList<>();
      TreeNode.collect(resultExprs_, Expr.IS_AGGREGATE, aggExprs_);
      if (havingPred_ != null) {
        havingPred_.collect(Expr.IS_AGGREGATE, aggExprs_);
      }
      if (sortInfo_ != null) {
        // TODO: Avoid evaluating aggs in ignored order-bys
        TreeNode.collect(sortInfo_.getSortExprs(), Expr.IS_AGGREGATE,
            aggExprs_);
      }
    }

    private void rewriteCountDistinct() {
      // Optionally rewrite all count(distinct <expr>) into equivalent NDV() calls.
      if (!analyzer_.getQueryCtx().client_request.query_options.appx_count_distinct) {
        return;
      }
      ndvSmap_ = new ExprSubstitutionMap();
      for (FunctionCallExpr aggExpr: aggExprs_) {
        if (!aggExpr.isDistinct()
            || !aggExpr.getFnName().getFunction().equals("count")
            || aggExpr.getParams().size() != 1) {
          continue;
        }
        FunctionCallExpr ndvFnCall =
            new FunctionCallExpr("ndv", aggExpr.getParams().exprs());
        ndvFnCall.analyzeNoThrow(analyzer_);
        Preconditions.checkState(ndvFnCall.getType().equals(aggExpr.getType()));
        ndvSmap_.put(aggExpr, ndvFnCall);
      }
      // Replace all count(distinct <expr>) with NDV(<expr>).
      List<Expr> substAggExprs = Expr.substituteList(aggExprs_,
          ndvSmap_, analyzer_, false);
      aggExprs_.clear();
      for (Expr aggExpr: substAggExprs) {
        Preconditions.checkState(aggExpr instanceof FunctionCallExpr);
        aggExprs_.add((FunctionCallExpr) aggExpr);
      }
    }

    private void buildAggregateExprs() throws AnalysisException {
      // When DISTINCT aggregates are present, non-distinct (i.e. ALL) aggregates are
      // evaluated in two phases (see AggregateInfo for more details). In particular,
      // COUNT(c) in "SELECT COUNT(c), AGG(DISTINCT d) from R" is transformed to
      // "SELECT SUM(cnt) FROM (SELECT COUNT(c) as cnt from R group by d ) S".
      // Since a group-by expression is added to the inner query it returns no rows if
      // R is empty, in which case the SUM of COUNTs will return NULL.
      // However the original COUNT(c) should have returned 0 instead of NULL in this
      // case.
      // Therefore, COUNT([ALL]) is transformed into zeroifnull(COUNT([ALL]) if
      // i) There is no GROUP-BY clause, and
      // ii) Other DISTINCT aggregates are present.
      countAllMap_ = createCountAllMap();
      countAllMap_ = ExprSubstitutionMap.compose(ndvSmap_, countAllMap_, analyzer_);
      List<Expr> substitutedAggs =
          Expr.substituteList(aggExprs_, countAllMap_, analyzer_, false);
      aggExprs_.clear();
      TreeNode.collect(substitutedAggs, Expr.IS_AGGREGATE, aggExprs_);

      List<Expr> groupingExprs = groupingExprsCopy_;
      if (selectList_.isDistinct()) {
        // Create multiAggInfo for SELECT DISTINCT:
        // - all select list items turn into grouping exprs
        // - there are no aggregate exprs
        Preconditions.checkState(groupingExprsCopy_.isEmpty());
        Preconditions.checkState(aggExprs_.isEmpty());
        groupingExprs = Expr.cloneList(resultExprs_);
      }
      Expr.removeDuplicates(aggExprs_);
      Expr.removeDuplicates(groupingExprs);
      multiAggInfo_ = new MultiAggregateInfo(groupingExprs, aggExprs_);
      multiAggInfo_.analyze(analyzer_);
    }

    private void buildResultExprs() throws AnalysisException {
      ExprSubstitutionMap finalOutputSmap = multiAggInfo_.getOutputSmap();
      ExprSubstitutionMap combinedSmap =
          ExprSubstitutionMap.compose(countAllMap_, finalOutputSmap, analyzer_);

      // change select list, having and ordering exprs to point to agg output. We need
      // to reanalyze the exprs at this point.
      if (LOG.isTraceEnabled()) {
        LOG.trace("combined smap: " + combinedSmap.debugString());
        LOG.trace("desctbl: " + analyzer_.getDescTbl().debugString());
        LOG.trace("resultexprs: " + Expr.debugString(resultExprs_));
      }
      resultExprs_ = Expr.substituteList(resultExprs_, combinedSmap, analyzer_, false);
      if (LOG.isTraceEnabled()) {
        LOG.trace("post-agg selectListExprs: " + Expr.debugString(resultExprs_));
      }
      if (havingPred_ != null) {
        // Make sure the predicate in the HAVING clause does not contain a
        // subquery.
        Preconditions.checkState(!havingPred_.contains(
            Predicates.instanceOf(Subquery.class)));
        havingPred_ = havingPred_.substitute(combinedSmap, analyzer_, false);
        analyzer_.registerConjuncts(havingPred_, true);
        if (LOG.isTraceEnabled()) {
          LOG.trace("post-agg havingPred: " + havingPred_.debugString());
        }
      }
      if (sortInfo_ != null) {
        sortInfo_.substituteSortExprs(combinedSmap, analyzer_);
        if (LOG.isTraceEnabled()) {
          LOG.trace("post-agg orderingExprs: " +
              Expr.debugString(sortInfo_.getSortExprs()));
        }
      }
    }

    private void verifyAggregation() throws AnalysisException {
      // check that all post-agg exprs point to agg output
      for (int i = 0; i < selectList_.getItems().size(); ++i) {
        if (!resultExprs_.get(i).isBound(multiAggInfo_.getResultTupleId())) {
          SelectListItem selectListItem = selectList_.getItems().get(i);
          throw new AnalysisException(
              "select list expression not produced by aggregation output "
              + "(missing from GROUP BY clause?): "
              + selectListItem.toSql());
        }
      }
      if (orderByElements_ != null) {
        for (int i = 0; i < orderByElements_.size(); ++i) {
          if (!sortInfo_.getSortExprs().get(i).isBound(
              multiAggInfo_.getResultTupleId())) {
            throw new AnalysisException(
                "ORDER BY expression not produced by aggregation output "
                + "(missing from GROUP BY clause?): "
                + orderByElements_.get(i).getExpr().toSql());
          }
        }
      }
      if (havingPred_ != null) {
        if (!havingPred_.isBound(multiAggInfo_.getResultTupleId())) {
          throw new AnalysisException(
              "HAVING clause not produced by aggregation output "
              + "(missing from GROUP BY clause?): "
              + havingClause_.toSql());
        }
      }
    }

    /**
     * Create a map from COUNT([ALL]) -> zeroifnull(COUNT([ALL])) if
     * i) There is no GROUP-BY, and
     * ii) There are other distinct aggregates to be evaluated.
     * This transformation is necessary for COUNT to correctly return 0
     * for empty input relations.
     */
    private ExprSubstitutionMap createCountAllMap()
        throws AnalysisException {
      ExprSubstitutionMap scalarCountAllMap = new ExprSubstitutionMap();

      if (groupingExprs_ != null && !groupingExprs_.isEmpty()) {
        // There are grouping expressions, so no substitution needs to be done.
        return scalarCountAllMap;
      }

      com.google.common.base.Predicate<FunctionCallExpr> isNotDistinctPred =
          new com.google.common.base.Predicate<FunctionCallExpr>() {
            @Override
            public boolean apply(FunctionCallExpr expr) {
              return !expr.isDistinct();
            }
          };
      if (Iterables.all(aggExprs_, isNotDistinctPred)) {
        // Only [ALL] aggs, so no substitution needs to be done.
        return scalarCountAllMap;
      }

      com.google.common.base.Predicate<FunctionCallExpr> isCountPred =
          new com.google.common.base.Predicate<FunctionCallExpr>() {
            @Override
            public boolean apply(FunctionCallExpr expr) {
              return expr.getFnName().getFunction().equals("count");
            }
          };

      Iterable<FunctionCallExpr> countAllAggs =
          Iterables.filter(aggExprs_, Predicates.and(isCountPred, isNotDistinctPred));
      for (FunctionCallExpr countAllAgg: countAllAggs) {
        // Replace COUNT(ALL) with zeroifnull(COUNT(ALL))
        List<Expr> zeroIfNullParam = Lists.newArrayList(countAllAgg.clone());
        FunctionCallExpr zeroIfNull =
            new FunctionCallExpr("zeroifnull", zeroIfNullParam);
        zeroIfNull.analyze(analyzer_);
        scalarCountAllMap.put(countAllAgg, zeroIfNull);
      }

      return scalarCountAllMap;
    }

    /**
     * If the select list contains AnalyticExprs, create AnalyticInfo and substitute
     * AnalyticExprs using the AnalyticInfo's smap.
     */
    private void createAnalyticInfo()
        throws AnalysisException {
      // collect AnalyticExprs from the SELECT and ORDER BY clauses
      List<AnalyticExpr> analyticExprs = new ArrayList<>();
      TreeNode.collect(resultExprs_, AnalyticExpr.class, analyticExprs);
      if (sortInfo_ != null) {
        TreeNode.collect(sortInfo_.getSortExprs(), AnalyticExpr.class,
            analyticExprs);
      }
      if (analyticExprs.isEmpty()) return;
      ExprSubstitutionMap rewriteSmap = new ExprSubstitutionMap();
      for (Expr expr: analyticExprs) {
        AnalyticExpr toRewrite = (AnalyticExpr)expr;
        Expr newExpr = AnalyticExpr.rewrite(toRewrite);
        if (newExpr != null) {
          newExpr.analyze(analyzer_);
          if (!rewriteSmap.containsMappingFor(toRewrite)) {
            rewriteSmap.put(toRewrite, newExpr);
          }
        }
      }
      if (rewriteSmap.size() > 0) {
        // Substitute the exprs with their rewritten versions.
        List<Expr> updatedAnalyticExprs =
            Expr.substituteList(analyticExprs, rewriteSmap, analyzer_, false);
        // This is to get rid the original exprs which have been rewritten.
        analyticExprs.clear();
        // Collect the new exprs introduced through the rewrite and the
        // non-rewrite exprs.
        TreeNode.collect(updatedAnalyticExprs, AnalyticExpr.class, analyticExprs);
      }

      analyticInfo_ = AnalyticInfo.create(analyticExprs, analyzer_);

      ExprSubstitutionMap smap = analyticInfo_.getSmap();
      // If 'exprRewritten' is true, we have to compose the new smap with
      // the existing one.
      if (rewriteSmap.size() > 0) {
        smap = ExprSubstitutionMap.compose(
            rewriteSmap, analyticInfo_.getSmap(), analyzer_);
      }
      // change select list and ordering exprs to point to analytic output. We need
      // to reanalyze the exprs at this point.
      resultExprs_ = Expr.substituteList(resultExprs_, smap, analyzer_, false);
      if (LOG.isTraceEnabled()) {
        LOG.trace("post-analytic selectListExprs: " + Expr.debugString(resultExprs_));
      }
      if (sortInfo_ != null) {
        sortInfo_.substituteSortExprs(smap, analyzer_);
        if (LOG.isTraceEnabled()) {
          LOG.trace("post-analytic orderingExprs: " +
              Expr.debugString(sortInfo_.getSortExprs()));
        }
      }
    }

    private void buildColumnLineageGraph() {
      ColumnLineageGraph graph = analyzer_.getColumnLineageGraph();
      if (multiAggInfo_ != null && multiAggInfo_.hasAggregateExprs()) {
        graph.addDependencyPredicates(multiAggInfo_.getGroupingExprs());
      }
      if (sortInfo_ != null && hasLimit()) {
        // When there is a LIMIT clause in conjunction with an ORDER BY, the
        // ordering exprs must be added in the column lineage graph.
        graph.addDependencyPredicates(sortInfo_.getSortExprs());
      }
    }
  }

  /**
   * Marks all unassigned join predicates as well as exprs in aggInfo and sortInfo.
   */
  @Override
  public void materializeRequiredSlots(Analyzer analyzer) {
    // Mark unassigned join predicates. Some predicates that must be evaluated by a join
    // can also be safely evaluated below the join (picked up by getBoundPredicates()).
    // Such predicates will be marked twice and that is ok.
    List<Expr> unassigned =
        analyzer.getUnassignedConjuncts(getTableRefIds(), true);
    List<Expr> unassignedJoinConjuncts = new ArrayList<>();
    for (Expr e: unassigned) {
      if (analyzer.evalAfterJoin(e)) unassignedJoinConjuncts.add(e);
    }
    List<Expr> baseTblJoinConjuncts =
        Expr.substituteList(unassignedJoinConjuncts, baseTblSmap_, analyzer, false);
    materializeSlots(analyzer, baseTblJoinConjuncts);

    if (evaluateOrderBy_) {
      // mark ordering exprs before marking agg/analytic exprs because they could contain
      // agg/analytic exprs that are not referenced anywhere but the ORDER BY clause
      sortInfo_.materializeRequiredSlots(analyzer, baseTblSmap_);
    }

    if (hasAnalyticInfo()) {
      // Mark analytic exprs before marking agg exprs because they could contain agg
      // exprs that are not referenced anywhere but the analytic expr.
      // Gather unassigned predicates and mark their slots. It is not desirable
      // to account for propagated predicates because if an analytic expr is only
      // referenced by a propagated predicate, then it's better to not materialize the
      // analytic expr at all.
      List<TupleId> tids = new ArrayList<>();
      getMaterializedTupleIds(tids); // includes the analytic tuple
      List<Expr> conjuncts = analyzer.getUnassignedConjuncts(tids, false);
      materializeSlots(analyzer, conjuncts);
      analyticInfo_.materializeRequiredSlots(analyzer, baseTblSmap_);
    }

    if (multiAggInfo_ != null) {
      // Mark all agg slots required for conjunct evaluation as materialized before
      // calling MultiAggregateInfo.materializeRequiredSlots().
      List<Expr> conjuncts = multiAggInfo_.collectConjuncts(analyzer, false);
      materializeSlots(analyzer, conjuncts);
      multiAggInfo_.materializeRequiredSlots(analyzer, baseTblSmap_);
    }
  }

  public List<TupleId> getTableRefIds() {
    List<TupleId> result = new ArrayList<>();
    for (TableRef ref: fromClause_) {
      result.add(ref.getId());
    }
    return result;
  }

  /**
   * If given expr is rewritten into an integer literal, then return the original expr,
   * otherwise return the rewritten expr.
   * Used for GROUP BY, ORDER BY, and HAVING where we don't want to create an ordinal
   * from a constant arithmetic expr, e.g. 1 * 2 =/=> 2
   */
  private Expr rewriteCheckOrdinalResult(ExprRewriter rewriter, Expr expr)
      throws AnalysisException {
    Expr rewrittenExpr = rewriter.rewrite(expr, analyzer_);
    if (Expr.IS_LITERAL.apply(rewrittenExpr) && rewrittenExpr.getType().isIntegerType()) {
      return expr;
    } else {
      return rewrittenExpr;
    }
  }

  @Override
  public void rewriteExprs(ExprRewriter rewriter) throws AnalysisException {
    Preconditions.checkState(isAnalyzed());
    selectList_.rewriteExprs(rewriter, analyzer_);
    for (TableRef ref: fromClause_.getTableRefs()) ref.rewriteExprs(rewriter, analyzer_);
    if (whereClause_ != null) {
      whereClause_ = rewriter.rewrite(whereClause_, analyzer_);
      // Also rewrite exprs in the statements of subqueries.
      List<Subquery> subqueryExprs = new ArrayList<>();
      whereClause_.collect(Subquery.class, subqueryExprs);
      for (Subquery s: subqueryExprs) s.getStatement().rewriteExprs(rewriter);
    }
    if (havingClause_ != null) {
      havingClause_ = rewriteCheckOrdinalResult(rewriter, havingClause_);
    }
    if (groupingExprs_ != null) {
      for (int i = 0; i < groupingExprs_.size(); ++i) {
        groupingExprs_.set(i, rewriteCheckOrdinalResult(
            rewriter, groupingExprs_.get(i)));
      }
    }
    if (orderByElements_ != null) {
      for (OrderByElement orderByElem: orderByElements_) {
        orderByElem.setExpr(rewriteCheckOrdinalResult(rewriter, orderByElem.getExpr()));
      }
    }
  }

  @Override
  public String toSql(ToSqlOptions options) {
    // Return the SQL string before inline-view expression substitution.
    if (!options.showRewritten() && sqlString_ != null) return sqlString_;

    StringBuilder strBuilder = new StringBuilder();
    if (withClause_ != null) {
      strBuilder.append(withClause_.toSql(options));
      strBuilder.append(" ");
    }

    // Select list
    strBuilder.append("SELECT ");
    if (selectList_.isDistinct()) {
      strBuilder.append("DISTINCT ");
    }
    if (selectList_.hasPlanHints()) {
      strBuilder.append(ToSqlUtils.getPlanHintsSql(options, selectList_.getPlanHints()))
          .append(" ");
    }
    for (int i = 0; i < selectList_.getItems().size(); ++i) {
      strBuilder.append(selectList_.getItems().get(i).toSql(options));
      strBuilder.append((i+1 != selectList_.getItems().size()) ? ", " : "");
    }
    // From clause
    if (!fromClause_.isEmpty()) {
      strBuilder.append(fromClause_.toSql(options));
    }
    // Where clause
    if (whereClause_ != null) {
      strBuilder.append(" WHERE ");
      strBuilder.append(whereClause_.toSql(options));
    }
    // Group By clause
    if (groupingExprs_ != null) {
      strBuilder.append(" GROUP BY ");
      // Handle both analyzed (multiAggInfo_ != null) and unanalyzed cases.
      // Unanalyzed case us used to generate SQL such as for views.
      // See ToSqlUtils.getCreateViewSql().
      List<Expr> groupingExprs = multiAggInfo_ == null
          ? groupingExprs_ : multiAggInfo_.getGroupingExprs();
      for (int i = 0; i < groupingExprs.size(); ++i) {
        strBuilder.append(groupingExprs.get(i).toSql(options));
        strBuilder.append((i+1 != groupingExprs.size()) ? ", " : "");
      }
    }
    // Having clause
    if (havingClause_ != null) {
      strBuilder.append(" HAVING ");
      strBuilder.append(havingClause_.toSql(options));
    }
    // Order By clause
    if (orderByElements_ != null) {
      strBuilder.append(" ORDER BY ");
      for (int i = 0; i < orderByElements_.size(); ++i) {
        strBuilder.append(orderByElements_.get(i).toSql(options));
        strBuilder.append((i+1 != orderByElements_.size()) ? ", " : "");
      }
    }
    // Limit clause.
    strBuilder.append(limitElement_.toSql(options));
    return strBuilder.toString();
  }

  /**
   * If the select statement has a sort/top that is evaluated, then the sort tuple
   * is materialized. Else, if there is aggregation then the aggregate tuple id is
   * materialized. Otherwise, all referenced tables are materialized as long as they are
   * not semi-joined. If there are analytics and no sort, then the returned tuple
   * ids also include the logical analytic output tuple.
   */
  @Override
  public void getMaterializedTupleIds(List<TupleId> tupleIdList) {
    if (evaluateOrderBy_) {
      tupleIdList.add(sortInfo_.getSortTupleDescriptor().getId());
    } else if (multiAggInfo_ != null) {
      // Return the tuple id produced in the final aggregation step.
      tupleIdList.add(multiAggInfo_.getResultTupleId());
    } else {
      for (TableRef tblRef: fromClause_) {
        // Don't include materialized tuple ids from semi-joined table
        // refs (see IMPALA-1526)
        if (tblRef.getJoinOp().isLeftSemiJoin()) continue;
        // Remove the materialized tuple ids of all the table refs that
        // are semi-joined by the right semi/anti join.
        if (tblRef.getJoinOp().isRightSemiJoin()) tupleIdList.clear();
        tupleIdList.addAll(tblRef.getMaterializedTupleIds());
      }
    }
    // We materialize the agg tuple or the table refs together with the analytic tuple.
    if (hasAnalyticInfo() && !evaluateOrderBy_) {
      tupleIdList.add(analyticInfo_.getOutputTupleId());
    }
  }

  /**
   * C'tor for cloning.
   */
  private SelectStmt(SelectStmt other) {
    super(other);
    selectList_ = other.selectList_.clone();
    fromClause_ = other.fromClause_.clone();
    whereClause_ = (other.whereClause_ != null) ? other.whereClause_.clone() : null;
    groupingExprs_ =
        (other.groupingExprs_ != null) ? Expr.cloneList(other.groupingExprs_) : null;
    havingClause_ = (other.havingClause_ != null) ? other.havingClause_.clone() : null;
    colLabels_ = Lists.newArrayList(other.colLabels_);
    multiAggInfo_ = (other.multiAggInfo_ != null) ? other.multiAggInfo_.clone() : null;
    analyticInfo_ = (other.analyticInfo_ != null) ? other.analyticInfo_.clone() : null;
    sqlString_ = (other.sqlString_ != null) ? new String(other.sqlString_) : null;
    baseTblSmap_ = other.baseTblSmap_.clone();
  }

  @Override
  protected void collectTableRefs(List<TableRef> tblRefs, boolean fromClauseOnly) {
    super.collectTableRefs(tblRefs, fromClauseOnly);
    if (fromClauseOnly) {
      fromClause_.collectFromClauseTableRefs(tblRefs);
    } else {
      fromClause_.collectTableRefs(tblRefs);
    }
    if (!fromClauseOnly && whereClause_ != null) {
      // Collect TableRefs in WHERE-clause subqueries.
      List<Subquery> subqueries = new ArrayList<>();
      whereClause_.collect(Subquery.class, subqueries);
      for (Subquery sq: subqueries) {
        sq.getStatement().collectTableRefs(tblRefs, fromClauseOnly);
      }
    }
  }

  @Override
  public void collectInlineViews(Set<FeView> inlineViews) {
    // Impala currently supports sub queries only in FROM, WHERE & WITH clauses. Hence,
    // this function does not carry out any checks on HAVING clause.
    super.collectInlineViews(inlineViews);
    List<TableRef> fromTblRefs = getTableRefs();
    Preconditions.checkNotNull(inlineViews);
    for (TableRef fromTblRef : fromTblRefs) {
      if (fromTblRef instanceof InlineViewRef) {
        InlineViewRef inlineViewRef = (InlineViewRef) fromTblRef;
        inlineViews.add(inlineViewRef.getView());
        inlineViewRef.getViewStmt().collectInlineViews(inlineViews);
      }
    }
    if (whereClause_ != null) {
      for (Expr conjunct : whereClause_.getConjuncts()) {
        List<Subquery> whereSubQueries = Lists.newArrayList();
        conjunct.collect(Predicates.instanceOf(Subquery.class), whereSubQueries);
        if (whereSubQueries.size() == 0) continue;
        // Check that multiple subqueries do not exist in the same expression. This
        // should have been already caught by the analysis passes.
        Preconditions.checkState(whereSubQueries.size() == 1, "Invariant " +
            "violated: Multiple subqueries found in a single expression: " +
            conjunct.toSql());
        whereSubQueries.get(0).getStatement().collectInlineViews(inlineViews);
      }
    }
  }

  @Override
  public void reset() {
    super.reset();
    selectList_.reset();
    colLabels_.clear();
    fromClause_.reset();
    if (whereClause_ != null) whereClause_.reset();
    if (groupingExprs_ != null) Expr.resetList(groupingExprs_);
    if (havingClause_ != null) havingClause_.reset();
    havingPred_ = null;
    multiAggInfo_ = null;
    analyticInfo_ = null;
    baseTblSmap_.clear();
  }

  @Override
  public SelectStmt clone() { return new SelectStmt(this); }

  /**
   * Check if the stmt returns at most one row. This can happen
   * in the following cases:
   * 1. select stmt with a 'limit 1' clause
   * 2. select stmt with an aggregate function and no group by.
   * 3. select stmt with no from clause.
   * 4. select from an inline view that returns at most one row.
   *
   * This function may produce false negatives because the cardinality of the
   * result set also depends on the data a stmt is processing.
   */
  public boolean returnsSingleRow() {
    Preconditions.checkState(isAnalyzed());
    // limit 1 clause
    if (limitElement_ != null && hasLimit() && limitElement_.getLimit() == 1) return true;
    // No from clause (base tables or inline views)
    if (fromClause_.isEmpty()) return true;
    // Aggregation with no group by and no DISTINCT
    if (hasMultiAggInfo() && !hasGroupByClause() && !selectList_.isDistinct()) {
      return true;
    }
    // Select from an inline view that returns at most one row.
    List<TableRef> tableRefs = fromClause_.getTableRefs();
    if (tableRefs.size() == 1 && tableRefs.get(0) instanceof InlineViewRef) {
      InlineViewRef inlineView = (InlineViewRef)tableRefs.get(0);
      if (inlineView.queryStmt_ instanceof SelectStmt) {
        SelectStmt selectStmt = (SelectStmt)inlineView.queryStmt_;
        return selectStmt.returnsSingleRow();
      }
    }
    // In all other cases, return false.
    return false;
  }
}