private Expression MakeSubquery(Expression expression)
{
var newAlias = new TableAlias();
HashSet <TableAlias> aliases = DeclaredAliasGatherer.Gather(expression);
var decls = new List <ColumnDeclaration>();
foreach (TableAlias ta in aliases)
{
foreach (ColumnExpression col in columns[ta])
{
string name = decls.GetAvailableColumnName(col.Name);
var decl = new ColumnDeclaration(name, col, col.QueryType);
decls.Add(decl);
var newCol = new ColumnExpression(col.Type, col.QueryType, newAlias, col.Name);
map.Add(col, newCol);
}
}
return(new SelectExpression(newAlias, decls, expression, null));
}
protected override Expression VisitJoin(JoinExpression join)
{
join = (JoinExpression)base.VisitJoin(join);
if (join.Join == JoinType.CrossJoin && currentWhere != null)
{
// try to figure out which parts of the current where expression can be used for a join condition
HashSet <TableAlias> declaredLeft = DeclaredAliasGatherer.Gather(join.Left);
HashSet <TableAlias> declaredRight = DeclaredAliasGatherer.Gather(join.Right);
var declared = new HashSet <TableAlias>(declaredLeft.Union(declaredRight));
Expression[] exprs = currentWhere.Split(ExpressionType.And, ExpressionType.AndAlso);
List <Expression> good = exprs.Where(e => CanBeJoinCondition(e, declaredLeft, declaredRight, declared)).ToList();
if (good.Count > 0)
{
Expression condition = good.Join(ExpressionType.And);
join = UpdateJoin(join, JoinType.InnerJoin, join.Left, join.Right, condition);
Expression newWhere = exprs.Where(e => !good.Contains(e)).Join(ExpressionType.And);
currentWhere = newWhere;
}
}
return(join);
}
protected override Expression VisitJoin(JoinExpression join)
{
join = (JoinExpression)base.VisitJoin(join);
if (join.Join == JoinType.CrossApply || join.Join == JoinType.OuterApply)
{
if (join.Right is TableExpression)
{
return(new JoinExpression(JoinType.CrossJoin, join.Left, join.Right, null));
}
else
{
var select = join.Right as SelectExpression;
// Only consider rewriting cross apply if
// 1) right side is a select
// 2) other than in the where clause in the right-side select, no left-side declared aliases are referenced
// 3) and has no behavior that would change semantics if the where clause is removed (like groups, aggregates, take, skip, etc).
// Note: it is best to attempt this after redundant subqueries have been removed.
if (select != null && select.Take == null && select.Skip == null && !AggregateChecker.HasAggregates(select) && (select.GroupBy == null || select.GroupBy.Count == 0))
{
SelectExpression selectWithoutWhere = select.SetWhere(null);
HashSet <TableAlias> referencedAliases = ReferencedAliasGatherer.Gather(selectWithoutWhere);
HashSet <TableAlias> declaredAliases = DeclaredAliasGatherer.Gather(join.Left);
referencedAliases.IntersectWith(declaredAliases);
if (referencedAliases.Count == 0)
{
Expression where = select.Where;
select = selectWithoutWhere;
ProjectedColumns pc = ColumnProjector.ProjectColumns(language, where, select.Columns, select.Alias, DeclaredAliasGatherer.Gather(select.From));
select = select.SetColumns(pc.Columns);
where = pc.Projector;
JoinType jt = (where == null) ? JoinType.CrossJoin : (join.Join == JoinType.CrossApply ? JoinType.InnerJoin : JoinType.LeftOuter);
return(new JoinExpression(jt, join.Left, select, where));
}
}
}
}
return(join);
}
