PHP最有效的检查行是否存在的方法

Consider the following table

考虑下面的表

+-------------+---------+------+-----+---------+----------------+
| Field       | Type    | Null | Key | Default | Extra          |
+-------------+---------+------+-----+---------+----------------+
| id          | int(11) | NO   | PRI | NULL    | auto_increment |
| date        | date    | NO   |     | NULL    |                |
| sku         | varchar(10)    |     |         | NULL           |         
| impressions | int(11) | NO   |     | NULL    |                |
| sales       | int(11) | NO   |     | NULL    |                |
+-------------+---------+------+-----+---------+----------------+
+------