code: async function createColumn (args) {
      // get args object
      args = requireValidOptionalObject(args)
      // get create column sql
      var createColumnSql = sql.createColumn(this, args.column)
      // debug
      debug(createColumnSql)
      // attempt to create column
      await this.mysql().query(createColumnSql)
      // if new column was created then need to re-validate column data
      // to populate the new column
      this.needsValidate = true
      // add flag if d column was created to migrate values if needed
      if (args.column.name === 'd') {
          this.dColumnCreated = true
      }
  }
docs: @function createColumn
  
  create a new column on an existing table
  
  @param {object} args
  
  @returns {Promise}
  
  @throws {Error}