示例#1
0
        public static SelectExpression RemoveColumn(this SelectExpression select, ColumnDeclaration column)
        {
            List <ColumnDeclaration> columns = new List <ColumnDeclaration>(select.Columns);

            columns.Remove(column);
            return(select.SetColumns(columns));
        }
        protected override Expression VisitSelect(SelectExpression select)
        {
            select = (SelectExpression)base.VisitSelect(select);

            // look for redundant column declarations
            List <ColumnDeclaration> cols = select.Columns.OrderBy(c => c.Name).ToList();
            BitArray removed    = new BitArray(select.Columns.Count);
            bool     anyRemoved = false;

            for (int i = 0, n = cols.Count; i < n - 1; i++)
            {
                ColumnDeclaration ci  = cols[i];
                ColumnExpression  cix = ci.Expression as ColumnExpression;
                SqlType           qt  = cix != null ? cix.SqlType : ci.SqlType;
                ColumnExpression  cxi = new ColumnExpression(ci.Expression.Type, qt, select.Alias, ci.Name);
                for (int j = i + 1; j < n; j++)
                {
                    if (!removed.Get(j))
                    {
                        ColumnDeclaration cj = cols[j];
                        if (SameExpression(ci.Expression, cj.Expression))
                        {
                            // any reference to 'j' should now just be a reference to 'i'
                            ColumnExpression cxj = new ColumnExpression(cj.Expression.Type, qt, select.Alias, cj.Name);
                            this.map.Add(cxj, cxi);
                            removed.Set(j, true);
                            anyRemoved = true;
                        }
                    }
                }
            }
            if (anyRemoved)
            {
                List <ColumnDeclaration> newDecls = new List <ColumnDeclaration>();
                for (int i = 0, n = cols.Count; i < n; i++)
                {
                    if (!removed.Get(i))
                    {
                        newDecls.Add(cols[i]);
                    }
                }
                select = select.SetColumns(newDecls);
            }
            return(select);
        }
示例#3
0
        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
                {
                    SelectExpression 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    = TableAliasGatherer.Gather(join.Left);
                        referencedAliases.IntersectWith(declaredAliases);
                        if (referencedAliases.Count == 0)
                        {
                            Expression where = select.Where;
                            select           = selectWithoutWhere;
                            var pc = ColumnProjector.ProjectColumns(where, select.Columns, select.Alias, TableAliasGatherer.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);
        }