private SqlColumn FindColumnWithExpression(IEnumerable <SqlColumn> columns, SqlExpression expr)
{
foreach (SqlColumn c in columns)
{
if (c == expr)
{
return(c);
}
if (SqlComparer.AreEqual(c.Expression, expr))
{
return(c);
}
}
return(null);
}
internal override SqlSelect VisitSelect(SqlSelect select)
{
select.From = this.VisitSource(select.From);
select.Where = this.VisitExpression(select.Where);
for (int i = 0, n = select.GroupBy.Count; i < n; i++)
{
select.GroupBy[i] = this.VisitExpression(select.GroupBy[i]);
}
// remove duplicate group expressions
for (int i = select.GroupBy.Count - 1; i >= 0; i--)
{
for (int j = i - 1; j >= 0; j--)
{
if (SqlComparer.AreEqual(select.GroupBy[i], select.GroupBy[j]))
{
select.GroupBy.RemoveAt(i);
break;
}
}
}
select.Having = this.VisitExpression(select.Having);
for (int i = 0, n = select.OrderBy.Count; i < n; i++)
{
select.OrderBy[i].Expression = this.VisitExpression(select.OrderBy[i].Expression);
}
// remove duplicate order expressions
if (select.OrderBy.Count > 0)
{
this.equalizer.BuildEqivalenceMap(select.From);
for (int i = select.OrderBy.Count - 1; i >= 0; i--)
{
for (int j = i - 1; j >= 0; j--)
{
if (this.equalizer.AreEquivalent(select.OrderBy[i].Expression, select.OrderBy[j].Expression))
{
select.OrderBy.RemoveAt(i);
break;
}
}
}
}
select.Top = this.VisitExpression(select.Top);
select.Row = (SqlRow)this.Visit(select.Row);
select.Selection = this.VisitExpression(select.Selection);
return(select);
}
private static SqlExpression UnwrapTrivialCaseExpression(SqlSimpleCase sc)
{
if (sc.Whens.Count != 1)
{
return(sc);
}
if (!SqlComparer.AreEqual(sc.Expression, sc.Whens[0].Match))
{
return(sc);
}
SqlExpression result = sc.Whens[0].Value;
if (result.NodeType == SqlNodeType.SimpleCase)
{
return(UnwrapTrivialCaseExpression((SqlSimpleCase)result));
}
return(result);
}
internal bool AreEquivalent(SqlExpression e1, SqlExpression e2)
{
if (SqlComparer.AreEqual(e1, e2))
{
return(true);
}
SqlColumnRef cr1 = e1 as SqlColumnRef;
SqlColumnRef cr2 = e2 as SqlColumnRef;
if (cr1 != null && cr2 != null)
{
SqlColumn c1 = cr1.GetRootColumn();
SqlColumn c2 = cr2.GetRootColumn();
SqlColumn r;
return(this.map.TryGetValue(c1, out r) && r == c2);
}
return(false);
}
internal override SqlExpression VisitSimpleCase(SqlSimpleCase c)
{
c.Expression = this.VisitExpression(c.Expression);
int compareWhen = 0;
// Find the ELSE if it exists.
for (int i = 0, n = c.Whens.Count; i < n; i++)
{
if (c.Whens[i].Match == null)
{
compareWhen = i;
break;
}
}
c.Whens[compareWhen].Match = VisitExpression(c.Whens[compareWhen].Match);
c.Whens[compareWhen].Value = VisitExpression(c.Whens[compareWhen].Value);
// Compare each other when value to the compare when
List <SqlWhen> newWhens = new List <SqlWhen>();
bool allValuesLiteral = true;
for (int i = 0, n = c.Whens.Count; i < n; i++)
{
if (compareWhen != i)
{
SqlWhen when = c.Whens[i];
when.Match = this.VisitExpression(when.Match);
when.Value = this.VisitExpression(when.Value);
if (!SqlComparer.AreEqual(c.Whens[compareWhen].Value, when.Value))
{
newWhens.Add(when);
}
allValuesLiteral = allValuesLiteral && when.Value.NodeType == SqlNodeType.Value;
}
}
newWhens.Add(c.Whens[compareWhen]);
// Did everything reduce to a single CASE?
SqlExpression rewrite = TryToConsolidateAllValueExpressions(newWhens.Count, c.Whens[compareWhen].Value);
if (rewrite != null)
{
return(rewrite);
}
// Can it be a conjuction (or disjunction) of clauses?
rewrite = TryToWriteAsSimpleBooleanExpression(c.ClrType, c.Expression, newWhens, allValuesLiteral);
if (rewrite != null)
{
return(rewrite);
}
// Can any WHEN clauses be reduced to fall into the ELSE clause?
rewrite = TryToWriteAsReducedCase(c.ClrType, c.Expression, newWhens, c.Whens[compareWhen].Match, c.Whens.Count);
if (rewrite != null)
{
return(rewrite);
}
return(c);
}
