mysql怎麽把字段怎么改为允许为空???求解 alter table raytoon_1_company modify keywords NULL;alter table raytoon_1_company alter column keywords NULL;为什么都不行???ketwords不是关键字。 解决方案 » 免费领取超大流量手机卡,每月29元包185G流量+100分钟通话, 中国电信官方发货 mysql> desc x;+-------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+-------------+------+-----+---------+-------+| id | int(11) | NO | PRI | NULL | || c | varchar(10) | NO | | NULL | |+-------+-------------+------+-----+---------+-------+2 rows in set (0.19 sec)mysql> alter table x modify c varchar(10) null;Query OK, 0 rows affected (0.09 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc x;+-------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+-------------+------+-----+---------+-------+| id | int(11) | NO | PRI | NULL | || c | varchar(10) | YES | | NULL | |+-------+-------------+------+-----+---------+-------+2 rows in set (0.06 sec)mysql> mysql> alter table test3 modify a int null;Query OK, 0 rows affected (0.27 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc test3;+-------+---------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+---------+------+-----+---------+-------+| a | int(11) | YES | | NULL | |+-------+---------+------+-----+---------+-------+1 row in set (0.00 sec) 问一个关于group by 的问题 两个表的两列相减 myisam联合主键大批量插入效率问题请教 关于远程MYSQL服务器的问题 我的sql语句怎么不能得到正确结果,求大侠指点 postgres中大字符串用什么数据类型保存好? 为什么我在Mysql 中插入一条数据,然后紧接着select刚插入的记录的ID号,怎么select 出来是一个空值??? 这个例子算不可重复读还是虚读(幻读) serial 自增长列取值问题 mysql 怎么去掉null汇总 删除表B中 AID =表A中AID的记录 条件是表A的 S= 0 表B的id IN (1,2,3) 查询运行时间
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| c | varchar(10) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.19 sec)mysql> alter table x modify c varchar(10) null;
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> desc x;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| c | varchar(10) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.06 sec)mysql>
Query OK, 0 rows affected (0.27 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> desc test3;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| a | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)