/// <summary>
/// Repackages and passes an expression from an aggregate subquery back to the parent query.
/// </summary>
private SqlExpression CreateAggregateMappingExpression(SqlQuery parentQuery, SqlTable proxyTable, SqlExpression sqlExpr)
{
var subQuery = proxyTable.SubQuery.Queries[0];
string alias = parentQuery.AliasManager.CreateAlias("aggCol");
var groupByColumn = new SqlSelectItem
{
Expression = sqlExpr,
Alias = alias
};
subQuery.SelectClause.Items.Add(groupByColumn);
subQuery.GroupByClause.Expressions.Add(groupByColumn.Expression);
// Register an expression that can be used to access the group-by expression
string mappedSql = GetColumnSql(proxyTable, alias);
var mappedSqlExpr = new SqlExpression(mappedSql);
SqlExpression.CopyTransforms(sqlExpr, mappedSqlExpr);
mappedSqlExpr.DatabaseType = sqlExpr.DatabaseType;
return(mappedSqlExpr);
}