117 lines
4.8 KiB
C#
117 lines
4.8 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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using System.Diagnostics.CodeAnalysis;
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namespace System.Data.Linq.SqlClient {
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/// <summary>
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/// Find projection expressions on the right side of CROSS APPLY that do not
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/// depend exclusively on right side productions and move them outside of the
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/// CROSS APPLY by enclosing the CROSS APPLY with a new source.
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/// </summary>
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class SqlLiftIndependentRowExpressions {
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internal static SqlNode Lift(SqlNode node) {
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ColumnLifter cl = new ColumnLifter();
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node = cl.Visit(node);
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return node;
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}
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private class ColumnLifter : SqlVisitor {
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SelectScope expressionSink;
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SqlAggregateChecker aggregateChecker;
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internal ColumnLifter() {
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this.aggregateChecker = new SqlAggregateChecker();
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}
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class SelectScope {
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// Stack of projections lifted from the right to be pushed on the left.
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internal Stack<List<SqlColumn>> Lifted = new Stack<List<SqlColumn>>();
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internal IEnumerable<SqlAlias> LeftProduction;
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internal HashSet<SqlColumn> ReferencedExpressions = new HashSet<SqlColumn>();
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}
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internal override SqlSelect VisitSelect(SqlSelect select) {
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SelectScope s = expressionSink;
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// Don't lift through a TOP.
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if (select.Top != null) {
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expressionSink = null;
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}
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// Don't lift through a GROUP BY (or implicit GROUP BY).
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if (select.GroupBy.Count > 0 || this.aggregateChecker.HasAggregates(select)) {
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expressionSink = null;
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}
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// Don't lift through DISTINCT
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if (select.IsDistinct) {
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expressionSink = null;
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}
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if (expressionSink != null) {
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List<SqlColumn> keep = new List<SqlColumn>();
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List<SqlColumn> lift = new List<SqlColumn>();
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foreach (SqlColumn sc in select.Row.Columns) {
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bool referencesLeftsideAliases = SqlAliasesReferenced.ReferencesAny(sc.Expression, expressionSink.LeftProduction);
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bool isLockedExpression = expressionSink.ReferencedExpressions.Contains(sc);
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if (referencesLeftsideAliases && !isLockedExpression) {
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lift.Add(sc);
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} else {
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keep.Add(sc);
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}
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}
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select.Row.Columns.Clear();
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select.Row.Columns.AddRange(keep);
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if (lift.Count > 0) {
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expressionSink.Lifted.Push(lift);
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}
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}
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SqlSelect sel = base.VisitSelect(select);
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expressionSink = s;
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return sel;
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}
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internal override SqlExpression VisitColumnRef(SqlColumnRef cref) {
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if (expressionSink!=null) {
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expressionSink.ReferencedExpressions.Add(cref.Column);
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}
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return cref;
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}
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internal override SqlSource VisitJoin(SqlJoin join) {
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if (join.JoinType == SqlJoinType.CrossApply) {
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// Visit the left side as usual.
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join.Left = this.VisitSource(join.Left);
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// Visit the condition as usual.
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join.Condition = this.VisitExpression(join.Condition);
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// Visit the right, with the expressionSink set.
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SelectScope s = expressionSink;
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expressionSink = new SelectScope();
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expressionSink.LeftProduction = SqlGatherProducedAliases.Gather(join.Left);
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join.Right = this.VisitSource(join.Right);
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// Were liftable expressions found?
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SqlSource newSource = join;
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foreach (List<SqlColumn> cols in expressionSink.Lifted) {
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newSource = PushSourceDown(newSource, cols);
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}
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expressionSink = s;
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return newSource;
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}
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return base.VisitJoin(join);
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}
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[SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification="Unknown reason.")]
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private SqlSource PushSourceDown(SqlSource sqlSource, List<SqlColumn> cols) {
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SqlSelect ns = new SqlSelect(new SqlNop(cols[0].ClrType, cols[0].SqlType, sqlSource.SourceExpression), sqlSource, sqlSource.SourceExpression);
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ns.Row.Columns.AddRange(cols);
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return new SqlAlias(ns);
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}
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}
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}
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}
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