Golang Expression.String方法代码示例

// UpdateAggFields adds aggregate function resultfield to select result field list.
func (s *SelectList) UpdateAggFields(expr expression.Expression) (expression.Expression, error) {
	// We must add aggregate function to hidden select list
	// and use a position expression to fetch its value later.
	name := strings.ToLower(expr.String())
	index := -1
	for i := 0; i < s.HiddenFieldOffset; i++ {
		// only check origin name, e,g. "select sum(c1) as a from t order by sum(c1)"
		// or "select sum(c1) from t order by sum(c1)"
		if s.ResultFields[i].ColumnInfo.Name.L == name {
			index = i
			break
		}
	}

	if index == -1 {
		f := &field.Field{Expr: expr}
		s.AddField(f, nil)

		pos := len(s.Fields)

		s.AggFields[pos-1] = struct{}{}

		return &expression.Position{N: pos, Name: name}, nil
	}

	// select list has this field, use it directly.
	return &expression.Position{N: index + 1, Name: name}, nil
}

// UpdateAggFields adds aggregate function resultfield to select result field list.
func (s *SelectList) UpdateAggFields(expr expression.Expression, tableFields []*field.ResultField) (expression.Expression, error) {
	// For aggregate function, the name can be in table or select list.
	names := expressions.MentionedColumns(expr)

	for _, name := range names {
		if field.ContainFieldName(name, tableFields, field.DefaultFieldFlag) {
			continue
		}

		if field.ContainFieldName(name, s.ResultFields, field.DefaultFieldFlag) {
			continue
		}

		return nil, errors.Errorf("Unknown column '%s'", name)
	}

	// We must add aggregate function to hidden select list
	// and use a position expression to fetch its value later.
	exprName := expr.String()
	if !field.ContainFieldName(exprName, s.ResultFields, field.CheckFieldFlag) {
		f := &field.Field{Expr: expr, Name: exprName}
		resultField := &field.ResultField{Name: exprName}
		s.AddField(f, resultField)

		return &expressions.Position{N: len(s.Fields), Name: exprName}, nil
	}

	return nil, nil
}

// CheckAmbiguous checks whether an identifier reference is ambiguous or not in select list.
// e,g, "select c1 as a, c2 as a from t group by a" is ambiguous,
// but "select c1 as a, c1 as a from t group by a" is not.
// "select c1 as a, c2 + 1 as a from t group by a" is not ambiguous too,
// If no ambiguous, -1 means expr refers none in select list, else an index for first match.
// CheckAmbiguous will break the check when finding first matching which is not an indentifier,
// or an index for an identifier field in the end, -1 means none found.
func (s *SelectList) CheckAmbiguous(expr expression.Expression) (int, error) {
	if _, ok := expr.(*expression.Ident); !ok {
		return -1, nil
	}

	name := expr.String()
	if field.IsQualifiedName(name) {
		// name is qualified, no need to check
		return -1, nil
	}

	//	select c1 as a, 1 as a, c2 as a from t order by a is not ambiguous.
	//	select c1 as a, c2 as a from t order by a is ambiguous.
	//	select 1 as a, c1 as a from t order by a is not ambiguous.
	//	select c1 as a, sum(c1) as a from t group by a is error.
	//	select c1 as a, 1 as a, sum(c1) as a from t group by a is not error.
	// 	so we will break the check if matching a none identifier field.
	lastIndex := -1
	// only check origin select list, no hidden field.
	for i := 0; i < s.HiddenFieldOffset; i++ {
		if !strings.EqualFold(s.ResultFields[i].Name, name) {
			continue
		}

		if _, ok := s.Fields[i].Expr.(*expression.Ident); !ok {
			// not identfier, return directly.
			return i, nil
		}

		if lastIndex == -1 {
			// first match, continue
			lastIndex = i
			continue
		}

		// check origin name, e,g. "select c1 as c2, c2 from t group by c2" is ambiguous.

		if s.ResultFields[i].ColumnInfo.Name.L != s.ResultFields[lastIndex].ColumnInfo.Name.L {
			return -1, errors.Errorf("refer %s is ambiguous", expr)
		}

		// check table name, e.g, "select t.c1, c1 from t group by c1" is not ambiguous.
		if s.ResultFields[i].TableName != s.ResultFields[lastIndex].TableName {
			return -1, errors.Errorf("refer %s is ambiguous", expr)
		}

		// TODO: check database name if possible.
	}

	return lastIndex, nil
}