func checkIdentAmbiguous(i *expression.Ident, selectList *plans.SelectList, clause clauseType) (int, error) {
index, err := selectList.CheckAmbiguous(i)
if err != nil {
return -1, errors.Errorf("Column '%s' in %s is ambiguous", i, clause)
} else if index == -1 {
return -1, nil
}
return index, nil
}
