code: func (p *Parser) parseAlias() (string, error) {
  	// Check if the next token is "AS". If not, then Unscan and exit.
  	if tok, _, _ := p.ScanIgnoreWhitespace(); tok != AS {
  		p.Unscan()
  		return "", nil
  	}
  
  	// Then we should have the alias identifier.
  	lit, err := p.ParseIdent()
  	if err != nil {
  		return "", err
  	}
  	return lit, nil
  }
docs: // parseAlias parses the "AS IDENT" alias for fields and dimensions.