private SqlFragment TryFlatteningGroupBy()

in EntityFramework/src/Generators/SelectGenerator.cs [75:131]
55 lines of code
19 McCabe index (conditional complexity)

    private SqlFragment TryFlatteningGroupBy(SqlFragment input)
    { 
      SelectStatement select = null;
      SelectStatement tmpFrag = null, tmpFrag2 = null, tmpFrag3 = null;
      InputFragment table = null;
      string objName = null, colName = null, queryName = null;
      // First part assert is a kind-of structure we are looking for
      tmpFrag = input as SelectStatement;
      if (tmpFrag == null) goto NoChanges;
      tmpFrag = ( tmpFrag ).From as SelectStatement;
      if (tmpFrag == null) goto NoChanges;
      queryName = tmpFrag.Name;
      if (tmpFrag.Columns.Count < 2) goto NoChanges;
      if (!(tmpFrag.Columns[0] is ColumnFragment)) goto NoChanges;
      colName = objName = (tmpFrag.Columns[0] as ColumnFragment).ActualColumnName;
      tmpFrag2 = tmpFrag.From as SelectStatement;
      if (tmpFrag2 == null) goto NoChanges;
      if (tmpFrag2.Columns.Count < 1 || !(tmpFrag2.Columns[0] is ColumnFragment)) goto NoChanges;
      if (string.CompareOrdinal(objName, tmpFrag2.Columns[0].ActualColumnName) != 0) goto NoChanges;
      if (tmpFrag.Columns[1].Literal == null ) goto NoChanges;
      tmpFrag2 = tmpFrag.Columns[1].Literal as SelectStatement;
      if (tmpFrag2 == null) goto NoChanges;
      if ((tmpFrag2.Columns.Count != 1) || !(tmpFrag2.Columns[0].Literal != null)) goto NoChanges;
      tmpFrag3 = tmpFrag2.From as SelectStatement;
      if (tmpFrag3 == null) goto NoChanges;
      table = tmpFrag3.From as InputFragment;
      if (table == null) goto NoChanges;
      FunctionFragment func = tmpFrag2.Columns[0].Literal as FunctionFragment;
      if( tmpFrag3.Columns.Count != 1 || !( tmpFrag3.Columns[ 0 ] is ColumnFragment )) goto NoChanges;
      if (func == null) goto NoChanges;
      // Yes it is the kind-of type we like, then optimize it
      select = new SelectStatement(this);      
      table.Name = null;
      string tableName = null;
      TableFragment t = tmpFrag3.From as TableFragment;
      if (t == null)
        tableName = tmpFrag3.Columns[0].TableName;
      else
        tableName = t.Table;
      select.From = table;
      select.Columns.Add(new ColumnFragment(tableName, colName));
      select.Columns.Add(new ColumnFragment(tableName, "C0")
      {
        ColumnAlias = "C1",
        Literal = new FunctionFragment() {
          Argument = new ColumnFragment(tableName, tmpFrag3.Columns[0].ActualColumnName),
          Distinct = tmpFrag3.IsDistinct,
          Name = func.Name
        }
      });
      select.Wrap(null); 
      select.Name = queryName;
      select.AddGroupBy(select.Columns[0]);
      (input as SelectStatement).From = select;
NoChanges:
      return input;
    }