sql - sql查询中%%%的含义？

Question

我熟悉这种查询:

select * from tableA where foo like '%bar%'

但是今天我在一些遗留代码中遇到了三个相邻的百分比符号，如下所示:

select * from tableA where foo like '%%%'

当 foo 是字符串类型(varchar 等)时，这个查询在 mssql 和 oracle 上似乎都有效，但当 foo 是数字时它会失败。

知道这意味着什么吗？

编辑:抱歉原始问题中的错字，查询使用 LIKE 运算符。

Answer 1

结果在 mysql 中它匹配everthing:

mysql> create database foo;
Query OK, 1 row affected (0.06 sec)

mysql> use foo;
Database changed

mysql> create table foo ( bar char(20) );
Query OK, 0 rows affected (0.06 sec)

mysql> desc foo;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| bar   | char(20) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
1 row in set (0.00 sec)

mysql> insert into foo values ('endwith%');
Query OK, 1 row affected (0.05 sec)

mysql> insert into foo values ('%startwith');
Query OK, 1 row affected (0.00 sec)

mysql> insert into foo values ('cont%ins');
Query OK, 1 row affected (0.00 sec)

mysql> insert into foo values ('doesnotcontain');
Query OK, 1 row affected (0.00 sec)

mysql> select * from foo where bar like '%%%';
+----------------+
| bar            |
+----------------+
| endwith%       |
| %startwith     |
| cont%ins       |
| doesnotcontain |
+----------------+
4 rows in set (0.00 sec)