如何update一个字段的值为null??不是空串'',也不是字符串'null'。谁知道???
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+------+---------------+
| id | c1 |
+------+---------------+
| 20 | http://123123 |
+------+---------------+
1 row in set (0.00 sec)mysql> update t5 set c1=null where id=20;
Query OK, 1 row affected (0.16 sec)
Rows matched: 1 Changed: 1 Warnings: 0mysql> select * from t5 where id=20;
+------+------+
| id | c1 |
+------+------+
| 20 | NULL |
+------+------+
1 row in set (0.00 sec)mysql>
update tt set f1=null