Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Linq/SqlClient/Query/SqlUnionizer.cs

@@ -0,0 +1,63 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Data.Linq.SqlClient {
+    internal class SqlUnionizer {
+        internal static SqlNode Unionize(SqlNode node) {
+            return new Visitor().Visit(node);
+        }
+
+        class Visitor : SqlVisitor {
+            internal override SqlSelect  VisitSelect(SqlSelect select) {
+ 	            base.VisitSelect(select);
+
+                // enforce exact ordering of columns in union selects
+                SqlUnion union = this.GetUnion(select.From);
+                if (union != null) {
+                    SqlSelect sleft = union.Left as SqlSelect;
+                    SqlSelect sright = union.Right as SqlSelect;
+                    if (sleft != null & sright != null) {
+                        // preset ordinals to high values (so any unreachable column definition is ordered last)
+                        for (int i = 0, n = sleft.Row.Columns.Count; i < n; i++) {
+                            sleft.Row.Columns[i].Ordinal = select.Row.Columns.Count + i;
+                        }
+                        for (int i = 0, n = sright.Row.Columns.Count; i < n; i++) {
+                            sright.Row.Columns[i].Ordinal = select.Row.Columns.Count + i;
+                        }
+                        // next assign ordinals to all direct columns in subselects
+                        for (int i = 0, n = select.Row.Columns.Count; i < n; i++) {
+                            SqlExprSet es = select.Row.Columns[i].Expression as SqlExprSet;
+                            if (es != null) {
+                                for (int e = 0, en = es.Expressions.Count; e < en; e++) {
+                                    SqlColumnRef cr = es.Expressions[e] as SqlColumnRef;
+                                    if (cr != null && e >= select.Row.Columns.Count) {
+                                        cr.Column.Ordinal = i;
+                                    }
+                                }
+                            }
+                        }
+                        // next sort columns in left & right subselects
+                        Comparison<SqlColumn> comp = (x,y) => x.Ordinal - y.Ordinal;
+                        sleft.Row.Columns.Sort(comp);
+                        sright.Row.Columns.Sort(comp);
+                    }
+                }
+
+                return select;
+            }
+
+            [SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification="Unknown reason.")]
+            private SqlUnion GetUnion(SqlSource source) {
+                SqlAlias alias = source as SqlAlias;
+                if (alias != null) {
+                    SqlUnion union = alias.Node as SqlUnion;
+                    if (union != null)
+                        return union;
+                }
+                return null;
+            }
+        }
+    }
+}