public SelectSql columns(String... columns) {
        if (columns == null || columns.length == 0) {
            throw new JdbcException("columns must have length");
        }

        String split = "";
        for (String column : columns) {
            sql.append(split);
            split = ",";
            sql.append(column.trim()).append(" ");
        }
        return this;
    }
@author Robert HG (254963746@qq.com) on 3/8/16.
lts-core/src/main/java/com/github/ltsopensource/store/jdbc/builder/SelectSql.java