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//---------------------------------------------------------------------
// <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
}
}