code: function createColumn (model, column) {
      // build query
      var sql = `ALTER TABLE ${quoteName(model.name)} ADD COLUMN ${createTableColumn(model, column.name, column.spec)}`
      // add column first
      if (column.spec.first) {
          sql += ' FIRST'
      }
      // add column after
      if (column.spec.after) {
          sql += ` AFTER ${quoteName(column.spec.after)}`
      }
      // column has unique index
      if (column.spec.unique) {
          sql += `, ADD ${createTableUniqueKey(column.name, column.spec)}`
      }
      // column has non-unique index
      else if (column.spec.index) {
          sql += `, ADD ${createTableKey(column.name, column.spec)}`
      }
      // reture sql string
      return sql
  }
docs: @function createColumn
  
  generate sql for ALTER TABLE ADD COLUMN statement
  
  @param {ImmutableCoreModel} model
  @param {object} column
  
  @returns {string}
  
  @throws {Error}