public String queryString(String sql, Object... params) throws SQLException {
		return query(sql, new StringHandler(), params);
	}
public String queryString ( String sql , Object ... params ) throws SQLException { return query ( sql , new StringHandler ( ) , params ) ; }
查询单条单个字段记录,并将其转换为String

@param sql 查询语句
@param params 参数
@return 结果对象
@throws SQLException SQL执行异常