code: function (name, type, opts) {
              opts = opts || {};
              this.operations.push(merge({op:"setColumnType", name:name, type:type}, opts));
          }
docs: Modify a column's type in the DDL for the table.
  
  @example
  DB.alterTable("artist", function(){
  this.setColumnType("artist_name", 'char(10)');
  //=> ALTER COLUMN artist_name TYPE char(10)
  });