System.Data.SQLite

//---------------------------------------------------------------------
// <copyright file="SqlSelectStatement.cs" company="Microsoft">
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
//---------------------------------------------------------------------

namespace System.Data.SQLite
{
  using System;
  using System.Collections.Generic;
  using System.Diagnostics;
  using System.IO;
  using System.Text;
  using System.Data.Metadata.Edm;
  using System.Data.Common.CommandTrees;

  /// <summary>
  /// A SqlSelectStatement represents a canonical SQL SELECT statement.
  /// It has fields for the 6 main clauses
  /// <list type="number">
  /// <item>SELECT</item>
  /// <item>FROM</item>
  /// <item>WHERE</item>
  /// <item>GROUP BY</item>
  /// <item>ORDER BY</item>
  /// <item>LIMIT</item>
  /// </list>
  /// We do not have HAVING, since it does not correspond to anything in the DbCommandTree.
  /// Each of the fields is a SqlBuilder, so we can keep appending SQL strings
  /// or other fragments to build up the clause.
  ///
  /// We have a IsDistinct property to indicate that we want distict columns.
  /// This is given out of band, since the input expression to the select clause
  /// may already have some columns projected out, and we use append-only SqlBuilders.
  /// The DISTINCT is inserted when we finally write the object into a string.
  /// 
  /// Also, we have a Top property, which is non-null if the number of results should
  /// be limited to certain number. It is given out of band for the same reasons as DISTINCT.
  ///
  /// The FromExtents contains the list of inputs in use for the select statement.
  /// There is usually just one element in this - Select statements for joins may
  /// temporarily have more than one.
  ///
  /// If the select statement is created by a Join node, we maintain a list of
  /// all the extents that have been flattened in the join in AllJoinExtents
  /// <example>
  /// in J(j1= J(a,b), c)
  /// FromExtents has 2 nodes JoinSymbol(name=j1, ...) and Symbol(name=c)
  /// AllJoinExtents has 3 nodes Symbol(name=a), Symbol(name=b), Symbol(name=c)
  /// </example>
  ///
  /// If any expression in the non-FROM clause refers to an extent in a higher scope,
  /// we add that extent to the OuterExtents list.  This list denotes the list
  /// of extent aliases that may collide with the aliases used in this select statement.
  /// It is set by <see cref="SqlGenerator.Visit(DbVariableReferenceExpression)"/>.
  /// An extent is an outer extent if it is not one of the FromExtents.
  ///
  ///
  /// </summary>
  internal sealed class SqlSelectStatement : ISqlFragment
  {
    private bool isDistinct;

    /// <summary>
    /// Do we need to add a DISTINCT at the beginning of the SELECT
    /// </summary>
    internal bool IsDistinct
    {
      get { return isDistinct; }
      set { isDistinct = value; }
    }

    private List<Symbol> allJoinExtents;
    internal List<Symbol> AllJoinExtents
    {
      get { return allJoinExtents; }
      // We have a setter as well, even though this is a list,
      // since we use this field only in special cases.
      set { allJoinExtents = value; }
    }

    private List<Symbol> fromExtents;
    internal List<Symbol> FromExtents
    {
      get
      {
        if (null == fromExtents)
        {
          fromExtents = new List<Symbol>();
        }
        return fromExtents;
      }
    }

    private Dictionary<Symbol, bool> outerExtents;
    internal Dictionary<Symbol, bool> OuterExtents
    {
      get
      {
        if (null == outerExtents)
        {
          outerExtents = new Dictionary<Symbol, bool>();
        }
        return outerExtents;
      }
    }

    private TopClause top;
    internal TopClause Top
    {
      get { return top; }
      set
      {
        Debug.Assert(top == null, "SqlSelectStatement.Top has already been set");
        top = value;
      }
    }

    private SqlBuilder select = new SqlBuilder();
    internal SqlBuilder Select
    {
      get { return select; }
    }

    private SqlBuilder from = new SqlBuilder();
    internal SqlBuilder From
    {
      get { return from; }
    }


    private SqlBuilder where;
    internal SqlBuilder Where
    {
      get
      {
        if (null == where)
        {
          where = new SqlBuilder();
        }
        return where;
      }
    }

    private SqlBuilder groupBy;
    internal SqlBuilder GroupBy
    {
      get
      {
        if (null == groupBy)
        {
          groupBy = new SqlBuilder();
        }
        return groupBy;
      }
    }

    private SqlBuilder orderBy;
    public SqlBuilder OrderBy
    {
      get
      {
        if (null == orderBy)
        {
          orderBy = new SqlBuilder();
        }
        return orderBy;
      }
    }

    private string limit;
    public string Limit
    {
      get
      {
        return limit;
      }

      set
      {
        limit = value;
      }
    }

    private string offset;
    public string OffSet
    {
      get
      { return offset; }
      set
      { offset = value; }
    }

    //indicates whether it is the top most select statement, 
    // if not Order By should be omitted unless there is a corresponding TOP
    private bool isTopMost;
    internal bool IsTopMost
    {
      get { return this.isTopMost; }
      set { this.isTopMost = value; }
    }

    #region ISqlFragment Members

    /// <summary>
    /// Write out a SQL select statement as a string.
    /// We have to
    /// <list type="number">
    /// <item>Check whether the aliases extents we use in this statement have
    /// to be renamed.
    /// We first create a list of all the aliases used by the outer extents.
    /// For each of the FromExtents( or AllJoinExtents if it is non-null),
    /// rename it if it collides with the previous list.
    /// </item>
    /// <item>Write each of the clauses (if it exists) as a string</item>
    /// </list>
    /// </summary>
    /// <param name="writer"></param>
    /// <param name="sqlGenerator"></param>
    public void WriteSql(SqlWriter writer, SqlGenerator sqlGenerator)
    {
      #region Check if FROM aliases need to be renamed

      // Create a list of the aliases used by the outer extents
      // JoinSymbols have to be treated specially.
      List<string> outerExtentAliases = null;
      if ((null != outerExtents) && (0 < outerExtents.Count))
      {
        foreach (Symbol outerExtent in outerExtents.Keys)
        {
          JoinSymbol joinSymbol = outerExtent as JoinSymbol;
          if (joinSymbol != null)
          {
            foreach (Symbol symbol in joinSymbol.FlattenedExtentList)
            {
              if (null == outerExtentAliases) { outerExtentAliases = new List<string>(); }
              outerExtentAliases.Add(symbol.NewName);
            }
          }
          else
          {
            if (null == outerExtentAliases) { outerExtentAliases = new List<string>(); }
            outerExtentAliases.Add(outerExtent.NewName);
          }
        }
      }

      // An then rename each of the FromExtents we have
      // If AllJoinExtents is non-null - it has precedence.
      // The new name is derived from the old name - we append an increasing int.
      List<Symbol> extentList = this.AllJoinExtents ?? this.fromExtents;
      if (null != extentList)
      {
        foreach (Symbol fromAlias in extentList)
        {
          if ((null != outerExtentAliases) && outerExtentAliases.Contains(fromAlias.Name))
          {
            int i = sqlGenerator.AllExtentNames[fromAlias.Name];
            string newName;
            do
            {
              ++i;
              newName = fromAlias.Name + i.ToString(System.Globalization.CultureInfo.InvariantCulture);
            }
            while (sqlGenerator.AllExtentNames.ContainsKey(newName));
            sqlGenerator.AllExtentNames[fromAlias.Name] = i;
            fromAlias.NewName = newName;

            // Add extent to list of known names (although i is always incrementing, "prefix11" can
            // eventually collide with "prefix1" when it is extended)
            sqlGenerator.AllExtentNames[newName] = 0;
          }

          // Add the current alias to the list, so that the extents
          // that follow do not collide with me.
          if (null == outerExtentAliases) { outerExtentAliases = new List<string>(); }
          outerExtentAliases.Add(fromAlias.NewName);
        }
      }
      #endregion

      // Increase the indent, so that the Sql statement is nested by one tab.
      writer.Indent += 1; // ++ can be confusing in this context

      writer.Write("SELECT ");
      if (IsDistinct)
      {
        writer.Write("DISTINCT ");
      }

      if ((null == this.select) || this.Select.IsEmpty)
      {
        Debug.Assert(false);  // we have removed all possibilities of SELECT *.
        writer.Write("*");
      }
      else
      {
        this.Select.WriteSql(writer, sqlGenerator);
      }

      writer.WriteLine();
      writer.Write("FROM ");
      this.From.WriteSql(writer, sqlGenerator);

      if ((null != this.where) && !this.Where.IsEmpty)
      {
        writer.WriteLine();
        writer.Write("WHERE ");
        this.Where.WriteSql(writer, sqlGenerator);
      }

      if ((null != this.groupBy) && !this.GroupBy.IsEmpty)
      {
        writer.WriteLine();
        writer.Write("GROUP BY ");
        this.GroupBy.WriteSql(writer, sqlGenerator);
      }

      if ((null != this.orderBy) && !this.OrderBy.IsEmpty && (this.IsTopMost || this.Top != null))
      {
        writer.WriteLine();
        writer.Write("ORDER BY ");
        this.OrderBy.WriteSql(writer, sqlGenerator);
      }

      if ((null != this.limit) && this.limit.Length != 0) //&& (this.IsTopMost || this.Top != null))
      {
        writer.WriteLine();
        writer.Write(string.Format("LIMIT {0} ", limit));
      }

      if ((null != this.offset) && this.offset.Length != 0)// && (this.IsTopMost || this.Top != null))
      {

        if (this.limit != null && this.limit.Length != 0)
          writer.Write(string.Format("OFFSET {0} ", offset));
        else
        {
          writer.WriteLine();
          writer.Write(string.Format("LIMIT 8999999999999999999 OFFSET {0} ", offset));
        }

      }

      if (this.Top != null)
      {
        this.Top.WriteSql(writer, sqlGenerator);
      }


      --writer.Indent;
    }

    #endregion
  }
}

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