code: function columnName (columnName, throwError) {
      // if column name exists return
      if (defined(this.columns[columnName])) {
          return columnName
      }
      // if column name is alias the return full column name
      else if (defined(this.defaultColumnsInverse[columnName])) {
          return this.defaultColumnsInverse[columnName]
      }
      // column name does not exist - throw error if flag set
      else if (throwError) {
          throw new Error('no column '+columnName)
      }
  }
docs: @function columnName
  
  get correct column name from alias (e.g. id => fooId) - return undefined or
  throw error if column name does not exist
  
  @param {string} columnName
  @param {boolean} throwError
  
  @returns {undefined|string}
  
  @throws {Error}