Question

时间戳字段是DATETIME列，格式为2012-03-19 00:23:14。如何比较两行时间戳并找到较大的时间戳？我正在使用的下面的查询无效。

UPDATE report 1 status = 'time is larger' WHERE EXISTS 
  (SELECT ip_src, layer4_sport, timestamp FROM  
      (SELECT ip_src, layer4_sport, timestamp from report 1) AS tmpb  
   WHERE  report 1.layer4_sport = tmpb.layer4_sport 
   AND report 1.ip_src = tmpb.ip_src  
   AND  report 1.timestamp > tmpb.timestamp 
   GROUP BY ip_src, layer4_sport,  timestamp HAVING COUNT(*) = 2)

Answer 1

您可以尝试使用if语句来验证A时间戳是否大于B时间戳。

select if(UNIX_TIMESTAMP('2009-02-01 00:00:00') > UNIX_TIMESTAMP('2009-01-01 00:00:00'), true, false)

Answer 2

尝试使用UNIX_TIMESTAMP()，UNIX_TIMESTAMP(date)函数来比较两个时间戳。

http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_unix-timestamp

Answer 3

感谢上帝，现在查询还可以。

缺少的是表名后的SET语法，并且EXISTS中也应省略GROUP BY语法。

UPDATE report 1 SET status = 'time is larger' WHERE EXISTS 
  (SELECT ip_src, layer4_sport, timestamp FROM  
  (SELECT ip_src, layer4_sport, timestamp from report 1) AS tmpb  
   WHERE  report 1.layer4_sport = tmpb.layer4_sport 
   AND report 1.ip_src = tmpb.ip_src  
   AND  report 1.timestamp > tmpb.timestamp)

如何比较MySql中的两个时间戳？

3 个答案: