从第五行开始删除比第一行更早的行

Question

如何删除比第一行早但第五行开始的所有行（如果存在！）？ MySQL数据库的

布局：

user |post|timestamp 
Harry foo 1445275458 

（时间戳是CURRENT_TIMESTAMP）

Answer 1

鉴于由Drew无耻被盗和扩展该样品数据：

select t1.*, from_unixtime(tstamp) from t1; 

| id | fname | lname |  tstamp |  from_unixtime(tstamp) | 
|----|-------|-------|------------|---------------------------| 
| 1 | Harry | foo | 1445275458 | October, 19 2015 17:24:18 | 
| 2 | Harry | foo | 1445275457 | October, 19 2015 17:24:17 | 
| 3 | Harry | foo | 1445275456 | October, 19 2015 17:24:16 | 
| 4 | Harry | foo | 1445275455 | October, 19 2015 17:24:15 | 
| 5 | Harry | foo | 1445275454 | October, 19 2015 17:24:14 | 
| 6 | Harry | foo | 1445275453 | October, 19 2015 17:24:13 | 
| 7 | Harry | foo | 1445275452 | October, 19 2015 17:24:12 | 
| 8 | Harry | foo | 1345275458 | August, 18 2012 07:37:38 | 
| 9 | Harry | foo | 1435275458 | June, 25 2015 23:37:38 | 

与此查询

DELETE t1.* 
FROM t1 
LEFT JOIN (SELECT id FROM t1 ORDER BY tstamp DESC LIMIT 5) q ON t1.id = q.id 
WHERE q.id IS NULL 
AND t1.tstamp < NOW() - INTERVAL 1 DAY; 

你得到以下结果：

select t1.*, from_unixtime(tstamp) from t1; 

| id | fname | lname |  tstamp |  from_unixtime(tstamp) | 
|----|-------|-------|------------|---------------------------| 
| 1 | Harry | foo | 1445275458 | October, 19 2015 17:24:18 | 
| 2 | Harry | foo | 1445275457 | October, 19 2015 17:24:17 | 
| 3 | Harry | foo | 1445275456 | October, 19 2015 17:24:16 | 
| 4 | Harry | foo | 1445275455 | October, 19 2015 17:24:15 | 
| 5 | Harry | foo | 1445275454 | October, 19 2015 17:24:14 | 

• 看到它在sqlfiddle