Sql.Database.Logical.Optimizing

Unit
Source
Symbols

Symbol	Description
TIsSimpleColumn
TOptimizingSqlDatabase	Performs optimizations to the execution of SQL quries before they are sent to the decorated database.
TOptimizingSqlRewriteRule
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///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright (c) 2015 by Charta Software B.V.                           //
//  All rights reserved                                                  //
//                                                                       //
//  Version:  1.7.0.83525                                                //
//  Web site: https://pascal.chartasoftware.com/                         //
//                                                                       //
//  This code and information are provided "as is" without warranty of   //
//  any kind. Dissemination of this information or reproduction of       //
//  this material is strictly forbidden unless prior written permission  //
//  is obtained from Charta Software B.V..                               //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

unit Sql.Database.Logical.Optimizing;

interface

uses
  Boolean,
  Collection.List,
  Condition,
  Sql.Comparison,
  Sql.Database.Logical,
  Sql.Expression,
  Sql.Operator_.Binary,
  Sql.Result,
  Sql.Rewriter.Rule,
  Sql.Statement,
  Sql.Statement.ResultSet,
  Sql.Statement.ResultSet.Select,
  Text;

type
  TIsSimpleColumn = class(TCondition<TSqlResultSetColumn>)
  public
    function    Matches(const Column: TSqlResultSetColumn): TBoolean; override;
  end;

  TOptimizingSqlRewriteRule = class(TSqlRewriteRule)
  protected
    function    CanMoveLimitToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
    procedure   MoveLimitToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);
    procedure   CopyOrderByToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);

    function    CanMoveCountToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
    procedure   MoveCountToInnerSelect(OuterSelect, InnerSelect: TSqlSelect);

    function    CanMoveRestrictionsToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
    procedure   MoveRestrictionsToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect; const InnerIdentifier: TText);

    function    CanMergeOuterIntoInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
    procedure   MergeOuterIntoInnerSelect(OuterSelect, InnerSelect: TSqlSelect);

    function    IsLiteralBooleanExpression(Restriction: TSqlExpression; Value: TBoolean): TBoolean;
    function    ContainsLiteralBooleanExpression(Restrictions: TList<TSqlExpression>; Value: TBoolean): TBoolean;
    procedure   RemoveLiteralBooleanExpressions(Restrictions: TList<TSqlExpression>; Value: TBoolean);
    function    SimplifyAndAll(AndAll: TSqlAndAll): TSqlExpression;
    function    SimplifyOrAll(OrAll: TSqlOrAll): TSqlExpression;
    function    SimplifyOr(LogicalOr: TSqlLogicalOr): TSqlExpression;
    function    SimplifyAnd(LogicalAnd: TSqlLogicalAnd): TSqlExpression;
    procedure   SimplifyRestrictions(Restrictions: TList<TSqlExpression>);
    procedure   RewriteSelect(Select: TSqlSelect);

  public
    procedure   Rewrite(Context: TSqlRewriteContext; Expression: TSqlExpression); override;
  end;

  TOptimizingSqlDatabase = class(TLogicalSqlDatabase)
  private
    function    HandleDecoratedStatement(Statement: TSqlStatement; ResultMethod: TSqlQueryResultMethod): TSqlResult;

  public
    function    Query(Statement: TSqlStatement; ResultMethod: TSqlQueryResultMethod = sqrmStoreResult): TSqlResult; override;
  end;

implementation

uses
  Exception,
  Integer._32,
  Sql.Functions.Aggregate,
  Sql.Literal,
  Sql.Rewriter,
  Sql.Statement.DataManipulation,
  Sql.Table.Column.Reference,
  Sql.Table.Expression.ResultSetStatement;

{ TOptimizingSqlDatabase }

function TOptimizingSqlDatabase.Query(Statement: TSqlStatement; ResultMethod: TSqlQueryResultMethod): TSqlResult;
begin
  if (Statement is TSqlSelect) or (Statement is TSqlDelete) or (Statement is TSqlUpdate) then
    Result := HandleDecoratedStatement(Statement, ResultMethod)
  else
    Result := Database.Query(Statement, ResultMethod);
end;

function TOptimizingSqlDatabase.HandleDecoratedStatement(Statement: TSqlStatement; ResultMethod: TSqlQueryResultMethod): TSqlResult;
var
  WorkingCopy: TSqlStatement;
  Rewriter:    TSqlRewriter;
  RewriteRule: TSqlRewriteRule;
begin
  Statement.AddReference();

  WorkingCopy := Statement.CopyStatement();
  WorkingCopy.AddReference();

  RewriteRule := TOptimizingSqlRewriteRule.Create();

  Rewriter := TSqlRewriter.Create(RewriteRule);
  Rewriter.DecorateStatement(WorkingCopy);

  Result := Database.Query(WorkingCopy, ResultMethod);

  Rewriter.Free();
  RewriteRule.Free();

  Statement.ReleaseReference();
  WorkingCopy.ReleaseReference();
end;

{ TOptimizingSqlRewriteRule }

function TOptimizingSqlRewriteRule.CanMergeOuterIntoInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
begin
  Result := 
    not OuterSelect.Limit.HasEffect()
    and (OuterSelect.Restrictions.Count = 0)
    and (OuterSelect.GroupBy.Count = 0)
    and (OuterSelect.OrderBy.Count = 0)
    and (InnerSelect.GroupBy.Count = 0)
    and (InnerSelect.OrderBy.Count = 0)
    and OuterSelect.Columns.MatchesAll(TIsSimpleColumn.Create());
end;

function TOptimizingSqlRewriteRule.CanMoveCountToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
begin
  Result :=
    not InnerSelect.GroupsRows()
    and (OuterSelect.Columns.Count = 1)
    and (OuterSelect.Columns[0].Expression is TSqlCountAll)
    and (OuterSelect.Restrictions.Count = 0)
    and (OuterSelect.GroupBy.Count = 0); // TODO: GROUP BY does not need to be checked when the SELECT produces no duplicate rows, i.e. has a proper primary key
end;

function TOptimizingSqlRewriteRule.CanMoveLimitToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
begin
  Result :=
    OuterSelect.Limit.HasEffect()
    and (OuterSelect.Restrictions.Count = 0)
    and not OuterSelect.GroupsRows()
    and not InnerSelect.Limit.HasEffect()
    and (InnerSelect.OrderBy.Count = 0)
    and OuterSelect.OrderBy.MatchesAll(TSqlOrderByExpression.TIsColumnReference.Create());
end;

function TOptimizingSqlRewriteRule.CanMoveRestrictionsToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect): TBoolean;
begin
  Result :=
    not InnerSelect.Limit.HasEffect()
    and not InnerSelect.GroupsRows(); // TODO: The inner SELECT actually is allowed to group rows as long as the restrictions do not use the aggregated columns 
end;

function TOptimizingSqlRewriteRule.ContainsLiteralBooleanExpression(Restrictions: TList<TSqlExpression>; Value: TBoolean): TBoolean;
var
  Index: TInteger32;
begin
  Result := False;
  Index  := 0;

  while not Result and (Index < Restrictions.Count) do
  begin
    Result := IsLiteralBooleanExpression(Restrictions[Index], Value);
    Inc(Index);
  end;
end;

function TOptimizingSqlRewriteRule.IsLiteralBooleanExpression(Restriction: TSqlExpression; Value: TBoolean): TBoolean;
begin
  Result := (Restriction is TSqlLiteralBoolean) and ((Restriction as TSqlLiteralBoolean).Value = Value);
end;

procedure TOptimizingSqlRewriteRule.MergeOuterIntoInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);
begin
end;

procedure TOptimizingSqlRewriteRule.MoveCountToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);
begin
  InnerSelect.Columns.Clear();
  InnerSelect.Columns.Add(TSqlResultSetColumn.Create(TSqlCountAll.Create()));
  InnerSelect.OrderBy.Clear();

  OuterSelect.Columns.Clear();
  OuterSelect.Columns.Add(TSqlResultSetColumn.Create(TSqlAllColumns.Create()));
end;

procedure TOptimizingSqlRewriteRule.MoveLimitToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);
begin
  InnerSelect.Limit.AssignFrom(OuterSelect.Limit);
  OuterSelect.Limit.Clear();
end;

procedure TOptimizingSqlRewriteRule.CopyOrderByToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect);
var
  Index:                  TInteger32;
  OuterOrderByExpression: TSqlOrderByExpression;
  OuterOrderByColumn:     TSqlTableColumnReference;
  InnerOrderByColumn:     TSqlResultSetColumn;
begin
  for Index := 0 to OuterSelect.OrderBy.Count - 1 do
  begin
    OuterOrderByExpression := OuterSelect.OrderBy[Index];

    if OuterOrderByExpression.Expression is TSqlTableColumnReference then
    begin
      OuterOrderByColumn := OuterOrderByExpression.Expression as TSqlTableColumnReference;
      InnerOrderByColumn := InnerSelect.Columns.FindWithIdentifier(OuterOrderByColumn.Column.Identifier);

      InnerSelect.OrderBy.Add(TSqlOrderByExpression.Create(InnerOrderByColumn.Expression, OuterOrderByExpression.SortOrder));
    end
    else
      raise EException.Create('Cannot optimize ORDER BY');
  end;
end;

procedure TOptimizingSqlRewriteRule.MoveRestrictionsToInnerSelect(OuterSelect: TSqlSelect; InnerSelect: TSqlSelect; const InnerIdentifier: TText);
var
  Index:             TInteger32;
  OuterRestrictions: TList<TSqlExpression>;
  InnerRestrictions: TList<TSqlExpression>;
  Restriction:       TSqlExpression;
  BinaryOperator:    TSqlBinaryOperator;
  MovedRestriction:  TBoolean;
  AliasedExpression: TSqlExpression;
begin
  OuterRestrictions := OuterSelect.Restrictions;
  InnerRestrictions := InnerSelect.Restrictions;
  Index             := 0;

  while Index < OuterRestrictions.Count do
  begin
    Restriction      := OuterRestrictions[Index];
    MovedRestriction := False;

    // TODO: Not only binary operators can be moved
    if Restriction is TSqlBinaryOperator then
    begin
      BinaryOperator := Restriction as TSqlBinaryOperator;

      if
        (BinaryOperator.Left is TSqlTableColumnReference)
        and ((BinaryOperator.Left as TSqlTableColumnReference).Column.Scope.Identifier = InnerIdentifier) // TODO: Matching identifiers is probably not the best way, but it is the only thing we currently can do
        and (BinaryOperator.Right is TSqlLiteralValue) // TODO: This is a very limiting restriction 
      then
      begin
        AliasedExpression := InnerSelect.Columns.FindWithIdentifier((BinaryOperator.Left as TSqlTableColumnReference).Column.Identifier).Expression;
        BinaryOperator.Left := AliasedExpression;
        InnerRestrictions.Add(Restriction);
        OuterSelect.Restrictions.RemoveAt(Index);

        MovedRestriction := True;
      end;
    end;

    if not MovedRestriction then
      Inc(Index);
  end;
end;

procedure TOptimizingSqlRewriteRule.RemoveLiteralBooleanExpressions(Restrictions: TList<TSqlExpression>; Value: TBoolean);
var
  Index: TInteger32;
begin
  Index := Restrictions.Count - 1;

  while Index >= 0 do
  begin
    if IsLiteralBooleanExpression(Restrictions[Index], Value) then
      Restrictions.RemoveAt(Index);

    Dec(Index);
  end;
end;

procedure TOptimizingSqlRewriteRule.Rewrite(Context: TSqlRewriteContext; Expression: TSqlExpression);
begin
  if Expression is TSqlSelect then
    RewriteSelect(Expression as TSqlSelect);
end;

procedure TOptimizingSqlRewriteRule.RewriteSelect(Select: TSqlSelect);
var
  InnerResultSetStatement: TSqlResultSetStatement;
  InnerSelect:             TSqlSelect;
  TableExpression:         TSqlResultSetStatementTableExpression;
begin
  SimplifyRestrictions(Select.Restrictions);

  if (Select.From.Count = 1) and (Select.From[0] is TSqlResultSetStatementTableExpression) then
  begin
    TableExpression         := Select.From[0] as TSqlResultSetStatementTableExpression;
    InnerResultSetStatement := TableExpression.Statement;

    if InnerResultSetStatement is TSqlSelect then
    begin
      InnerSelect := InnerResultSetStatement as TSqlSelect;

      if CanMoveRestrictionsToInnerSelect(Select, InnerSelect) then
        MoveRestrictionsToInnerSelect(Select, InnerSelect, TableExpression.Alias);

      if CanMoveLimitToInnerSelect(Select, InnerSelect) then
      begin
        CopyOrderByToInnerSelect(Select, InnerSelect);
        MoveLimitToInnerSelect(Select, InnerSelect);
      end;

      if CanMoveCountToInnerSelect(Select, InnerSelect) then
        MoveCountToInnerSelect(Select, InnerSelect);

      if CanMergeOuterIntoInnerSelect(Select, InnerSelect) then
        MergeOuterIntoInnerSelect(Select, InnerSelect);
    end;
  end;
end;

function TOptimizingSqlRewriteRule.SimplifyAnd(LogicalAnd: TSqlLogicalAnd): TSqlExpression;
begin
  if IsLiteralBooleanExpression(LogicalAnd.Left, False) or IsLiteralBooleanExpression(LogicalAnd.Right, False) then
    Result := TSqlLiteralBoolean.Create(False)
  else if IsLiteralBooleanExpression(Logicaland.Left, True) then
    Result := LogicalAnd.Right
  else if IsLiteralBooleanExpression(LogicalAnd.Right, True) then
    Result := LogicalAnd.Left
  else
    Result := LogicalAnd;
end;

function TOptimizingSqlRewriteRule.SimplifyAndAll(AndAll: TSqlAndAll): TSqlExpression;
begin
  SimplifyRestrictions(AndAll.Expressions);
  RemoveLiteralBooleanExpressions(AndAll.Expressions, True);

  case AndAll.Expressions.Count of
    0: Result := TSqlLiteralBoolean.Create(True);
    1: Result := AndAll.Expressions[0];
    else
    begin
      if ContainsLiteralBooleanExpression(AndAll.Expressions, False) then
        Result := TSqlLiteralBoolean.Create(False)
      else
        Result := AndAll;
    end;
  end;
end;

function TOptimizingSqlRewriteRule.SimplifyOr(LogicalOr: TSqlLogicalOr): TSqlExpression;
begin
  if IsLiteralBooleanExpression(LogicalOr.Left, True) or IsLiteralBooleanExpression(LogicalOr.Right, True) then
    Result := TSqlLiteralBoolean.Create(True)
  else if IsLiteralBooleanExpression(LogicalOr.Left, False) then
    Result := LogicalOr.Right
  else if IsLiteralBooleanExpression(LogicalOr.Right, False) then
    Result := LogicalOr.Left
  else
    Result := LogicalOr;
end;

function TOptimizingSqlRewriteRule.SimplifyOrAll(OrAll: TSqlOrAll): TSqlExpression;
begin
  RemoveLiteralBooleanExpressions(OrAll.Expressions, False);

  case OrAll.Expressions.Count of
    0: Result := TSqlLiteralBoolean.Create(False);
    1: Result := OrAll.Expressions[0];
    else
    begin
      if ContainsLiteralBooleanExpression(OrAll.Expressions, True) then
        Result := TSqlLiteralBoolean.Create(True)
      else
        Result := OrAll;
    end;
  end;
end;

procedure TOptimizingSqlRewriteRule.SimplifyRestrictions(Restrictions: TList<TSqlExpression>);
var
  Index:       TInteger32;
  Restriction: TSqlExpression;
begin
  for Index := 0 to Restrictions.Count - 1 do
  begin
    Restriction := Restrictions[Index];

    if Restriction is TSqlOrAll then
      Restrictions[Index] := SimplifyOrAll(Restriction as TSqlOrAll)
    else if Restriction is TSqlAndAll then
      Restrictions[Index] := SimplifyAndAll(Restriction as TSqlAndAll)
    else if Restriction is TSqlLogicalOr then
      Restrictions[Index] := SimplifyOr(Restriction as TSqlLogicalOr)
    else if Restriction is TSqlLogicalAnd then
      Restrictions[Index] := SimplifyAnd(Restriction as TSqlLogicalAnd);
  end;
end;

{ TIsSimpleColumn }

function TIsSimpleColumn.Matches(const Column: TSqlResultSetColumn): TBoolean;
begin
  Result := Column.Expression is TSqlTableColumnReference;
end;

end.