mysql - DELETE 占总数的百分比

Question

假设我想删除 10% 的行，是否有执行此操作的查询？

就像是：

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

Answer 1

如果您只需要大约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，由于生成随机数的开销，我不建议在非常大的数据集上使用它。

Answer 2

我将简单地返回过滤行的总数，通过 php 计算并将该值用作我的 DELETE 查询中的限制。

$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 是否允许像这样的高级查询：

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