关于一条语句的疑惑？？

ruochen-pb

当有null的时候，又如下

root@localhost:test 10:59:08>select * from test_char;
+--------+
| name   |
+--------+
| test-1 |
| test0  |
| NULL   |
| test2  |
|        |
| test4  |
+--------+
6 rows in set (0.00 sec)

root@localhost:test 10:59:23>select count(name='test' or null) as yyy from test_char;
+-----+
| yyy |
+-----+
|   0 |
+-----+
1 row in set (0.00 sec)

root@localhost:test 10:59:31>explain extended select count(name='test' or null) as yyy from test_char;
+----+-------------+-----------+------+---------------+------+---------+------+------+-------+
| id | select_type | table     | type | possible_keys | key  | key_len | ref  | rows | Extra |
+----+-------------+-----------+------+---------------+------+---------+------+------+-------+
|  1 | SIMPLE      | test_char | ALL  | NULL          | NULL | NULL    | NULL |    6 |       |
+----+-------------+-----------+------+---------------+------+---------+------+------+-------+
1 row in set, 1 warning (0.00 sec)

Note (Code 1003): select count(((`test`.`test_char`.`name` = _utf8'test') or NULL)) AS `yyy` from `test`.`test_char`

jinguanding

看来又要去研读下源代码了.....