Question

假设我想删除10％的行，是否有查询要执行此操作？

类似的东西：

DELETE FROM tbl WHERE conditions LIMIT (SELECT COUNT(*) FROM tbl WHERE conditions) * 0.1

Answer 1

如果你只需要大约 10％的行，没有特别的顺序，这应该可以解决问题：

DELETE FROM tbl WHERE RAND() <= 0.1

但是，由于产生随机数的开销，我不建议在非常大的数据集上使用它。

Answer 2

我只返回已过滤行的总量，通过php计算并在DELETE查询中将该值用作限制。

$query = mysql_query("SELECT COUNT(*) FROM tbl WHERE conditions");
$int = reset(mysql_fetch_array($query));
$int = round($int * 0.1);

mysql_query("DELETE FROM tbl WHERE conditions LIMIT {$int}");

我不确定DELETE是否允许使用高级查询，例如：

DELETE FROM (   SELECT h2.id
                FROM (  SELECT COUNT(*) AS total
                        FROM tbl
                        WHERE conditions) AS h
                JOIN (  SELECT *, @rownum := @rownum + 1 AS rownum
                        FROM tbl, (SELECT @rownum := 0) AS vars
                        WHERE conditions) AS h2
                ON '1'
                WHERE rownum < total * 0.1) AS h3

删除总计数百分比

2 个答案: