直到存储过程中的循环

Question

我正在尝试编写一个将触发相同选择查询的过程,直到结果数大于0.如果"间隔2小时"返回0记录,则应使用"间隔4小时"标准,如果仍有没有记录被提取,那么lastupdate> current_date()应该在where子句中使用.

这些是过程中使用的2个基本查询.

select sql_calc_found_rows id from sometable where lastupdate > date_sub(now(), interval 2 hour) limit 10;

select found_rows();
+--------------+
| found_rows() |
+--------------+
|           41 | 
+--------------+

以下程序是否正确？这是写SP的正确方法吗？我如何在PHP代码中使用结果？

delimiter $$
create procedure mytest3()
begin 

  declare myvar int;

 select sql_calc_found_rows id 
   from sometable 
  where lastupdate > date_sub(now(), interval 2 hour) 
  limit 10;

 select found_rows() into myvar;

if (myvar > 0) 
  then select 'Found in 2 hours';
else
  select sql_calc_found_rows id 
    from sometable 
   where lastupdate > date_sub(now(), interval 4 hour) 
   limit 10;

select found_rows() into myvar;

if (myvar > 0) 
  then select 'Found in 4 hours';
else 
  select sql_calc_found_rows id 
    from sometable 
   where lastupdate > current_date() 
   limit 10;
end if;
end if; 
end$$ 

Answer 1

我发现,当你在文本的标题和正文中都要求循环时,你真正要做的就是获取"在过去X小时内修改过的行"的列表,其中最小的X返回一些(非空)行集...

这是实现这一目标的一种方法:

delimiter $$
create procedure recently_modified_rows()
begin 

  declare tablelastupdate int; -- how many hours ago table was last updated.
  declare showperiod datetime; -- what time interval to show
  declare showtext  text;      -- text describing time interval

  select hour(timediff(now(), max(lastupdate))) into tablelastupdate
    from sometable;

  if(tablelastupdate < 2)
     set showperiod = time_sub(now(), interval 2 hours);
     set showtext = "modified in the last 2 hours";
  elseif (tablelastupdate < 4)
     set showperiod = time_sub(now(), interval 4 hours);
     set showtext = "modified in the last 4 hours";
  else
     set showperiod = current_date();
     set showtext = "modified today";
  end if

  select sql_calc_found_rows id, 
         showtext description
     from sometable 
     where lastupdate > showperiod 
     limit 10;

end$$

并从PHP调用它:

$query = mysql_query("call recently_modified_rows()") or die( mysql_error() );
$numrows = mysql_numrows($query);

if ($numrows != 0)
{
    /* print out what time interval we used */
    $description = mysql_result($query, 0, 'description');
    echo "Found $numrows rows $description";

    /* print out the rows */
    while ($row = mysql_fetch_array($query)) 
    {
       echo "Id: {$row['id']}";
    }

}
else 
{
    /* happens only if there were no records modified in any of the three versions */
    echo "no records were modified in the last 2 hours, 4 hours, or today";
}