public static SelectExpression Remove(SelectExpression outerSelect, IEnumerable <SelectExpression> selectsToRemove)
{
return((SelectExpression) new SubqueryRemover(selectsToRemove).Visit(outerSelect));
}
public static HashSet <ColumnExpression> Gather(HashSet <TableAlias> aliases, SelectExpression select)
{
var gatherer = new JoinColumnGatherer(aliases);
gatherer.Gather(select.Where);
return(gatherer.columns);
}
public static SelectExpression Remove(SelectExpression outerSelect, params SelectExpression[] selectsToRemove)
{
return(Remove(outerSelect, (IEnumerable <SelectExpression>)selectsToRemove));
}
protected override Expression VisitSelect(SelectExpression select)
{
// visit column projection first
ReadOnlyCollection <ColumnDeclaration> columns = select.Columns;
var wasRetained = this.retainAllColumns;
this.retainAllColumns = false;
List <ColumnDeclaration> alternate = null;
for (int i = 0, n = select.Columns.Count; i < n; i++)
{
ColumnDeclaration decl = select.Columns[i];
if (wasRetained || select.IsDistinct || IsColumnUsed(select.Alias, decl.Name))
{
Expression expr = this.Visit(decl.Expression);
if (expr != decl.Expression)
{
decl = new ColumnDeclaration(decl.Name, expr, decl.QueryType);
}
}
else
{
decl = null; // null means it gets omitted
}
if (decl != select.Columns[i] && alternate == null)
{
alternate = new List <ColumnDeclaration>();
for (int j = 0; j < i; j++)
{
alternate.Add(select.Columns[j]);
}
}
if (decl != null && alternate != null)
{
alternate.Add(decl);
}
}
if (alternate != null)
{
columns = alternate.AsReadOnly();
}
Expression take = this.Visit(select.Take);
Expression skip = this.Visit(select.Skip);
ReadOnlyCollection <Expression> groupbys = this.VisitExpressionList(select.GroupBy);
ReadOnlyCollection <OrderExpression> orderbys = this.VisitOrderBy(select.OrderBy);
Expression where = this.Visit(select.Where);
Expression from = this.Visit(select.From);
ClearColumnsUsed(select.Alias);
if (columns != select.Columns ||
take != select.Take ||
skip != select.Skip ||
orderbys != select.OrderBy ||
groupbys != select.GroupBy ||
where != select.Where ||
from != select.From)
{
select = new SelectExpression(select.Alias, columns, from, where, orderbys, groupbys, select.IsDistinct, skip, take, select.IsReverse);
}
this.retainAllColumns = wasRetained;
return(select);
}
private static bool CanMergeWithFrom(SelectExpression select, bool isTopLevel)
{
SelectExpression fromSelect = GetLeftMostSelect(select.From);
if (fromSelect == null)
{
return(false);
}
if (!IsColumnProjection(fromSelect))
{
return(false);
}
bool selHasNameMapProjection = IsNameMapProjection(select);
bool selHasOrderBy = select.OrderBy != null && select.OrderBy.Count > 0;
bool selHasGroupBy = select.GroupBy != null && select.GroupBy.Count > 0;
bool selHasAggregates = AggregateChecker.HasAggregates(select);
bool selHasJoin = select.From is JoinExpression;
bool frmHasOrderBy = fromSelect.OrderBy != null && fromSelect.OrderBy.Count > 0;
bool frmHasGroupBy = fromSelect.GroupBy != null && fromSelect.GroupBy.Count > 0;
bool frmHasAggregates = AggregateChecker.HasAggregates(fromSelect);
// both cannot have orderby
if (selHasOrderBy && frmHasOrderBy)
{
return(false);
}
// both cannot have groupby
if (selHasGroupBy && frmHasGroupBy)
{
return(false);
}
// these are distinct operations
if (select.IsReverse || fromSelect.IsReverse)
{
return(false);
}
// cannot move forward order-by if outer has group-by
if (frmHasOrderBy && (selHasGroupBy || selHasAggregates || select.IsDistinct))
{
return(false);
}
// cannot move forward group-by if outer has where clause
if (frmHasGroupBy /*&& (select.Where != null)*/) // need to assert projection is the same in order to move group-by forward
{
return(false);
}
// cannot move forward a take if outer has take or skip or distinct
if (fromSelect.Take != null && (select.Take != null || select.Skip != null || select.IsDistinct || selHasAggregates || selHasGroupBy || selHasJoin))
{
return(false);
}
// cannot move forward a skip if outer has skip or distinct
if (fromSelect.Skip != null && (select.Skip != null || select.IsDistinct || selHasAggregates || selHasGroupBy || selHasJoin))
{
return(false);
}
// cannot move forward a distinct if outer has take, skip, groupby or a different projection
if (fromSelect.IsDistinct && (select.Take != null || select.Skip != null || !selHasNameMapProjection || selHasGroupBy || selHasAggregates || (selHasOrderBy && !isTopLevel) || selHasJoin))
{
return(false);
}
if (frmHasAggregates && (select.Take != null || select.Skip != null || select.IsDistinct || selHasAggregates || selHasGroupBy || selHasJoin))
{
return(false);
}
return(true);
}
internal static bool IsInitialProjection(SelectExpression select)
{
return(select.From is TableExpression);
}
protected override Expression VisitSelect(SelectExpression select)
{
this.selects.Add(select);
return(select); // don't visit sub-queries
}
