-- 连接数据库mysql-h hostname-u username-p-- 查询所有表SHOWTABLES;-- 选择要修改的表USEdatabase_name;-- 删除原有的主键ALTERTABLEtable_nameDROPPRIMARYKEY;-- 添加新的主键ALTERTABLEtable_nameADDPRIMARYKEY(column_name); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 状态图 ...
mysql>ALTERTABLEtestalter_tblALTERiDROPDEFAULT; mysql>SHOWCOLUMNSFROMtestalter_tbl;+---+---+---+---+---+---+|Field|Type|Null|Key|Default|Extra|+---+---+---+---+---+---+|c|char(1)|YES||NULL|||i|int(11)|YES||NULL||+---+---+---+---+---+---+2rowsinset(0.00...
I have an exsiting table without primary key in mysql db. Now i wanna choose one column as the primary key. So what should i do? I tried "ALTER TABLE table_name PRIMARY KEY (newkey)", but it doesn't work. Thanks. Sorry, you can't reply to this topic. It has been closed. ...
mysql>CREATETABLEtestalter_tbl ->( ->iINT, ->cCHAR(1) ->); Query OK,0ROWSaffected(0.05sec) mysql>SHOWCOLUMNSFROMtestalter_tbl; +---+---+---+---+---+---+ |FIELD|TYPE|NULL|KEY|DEFAULT|Extra| +---+---+---+---+---+---+ |i|INT(11)|YES||NULL|| |c|CHAR(1)|YE...
根据索引的具体用途,MySQL 中的索引在逻辑上分为以下 5 类: 1) 普通索引 普通索引是最基本的索引类型,唯一任务是加快对数据的访问速度,没有任何限制。创建普通索引时,通常使用的关键字是 INDEX 或 KEY。 2) 唯一性索引 唯一性索引是不允许索引列具有相同索引值的索引。如果能确定某个数据列只包含彼此各不相同...
mysql alter无锁变更sql mysql加锁 锁的类型 MySQL 找那个根据加锁的范围,大致可以分成全局锁,表级锁和行级锁。 全局锁 全局锁,就是对整个数据库加锁。 加锁 flush tables with read lock 1. 解锁 unlock tables 1. 全局锁会让整个库处于只读状态,之后所有的更新操作都会被阻塞:...
id INT PRIMARY KEY, name VARCHAR(255) ); ALTER TABLE new_table ADD INDEX idx_name (name); DROP TABLE new_table; 这种组合使用极大地增强了数据库管理的灵活性和效率。 七、ALTER命令的性能优化 在高负载环境下,ALTER命令可能会对性能产生显著影响,因此需要进行性能优化。一种常见的做法是使用在线DDL操作...
For column definition changes using CHANGE or MODIFY, the definition must include the data type and all attributes that should apply to the new column, other than index attributes such as PRIMARY KEY or UNIQUE. Attributes present in the original definition but not specified for the new definition...
constraint_definition:约束的定义(如UNIQUE、PRIMARY KEY)。 示例: 向employees表中添加一个唯一约束: ALTERTABLEemployeesADDCONSTRAINTunique_emailUNIQUE(email); 6.2 删除约束 要从表中删除约束,可以使用以下语法: ALTERTABLEtable_nameDROPINDEX index_name; ...
I am sure the newkey is not NULL and no duplicates as well in that field. The error message is quite typical: "You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax ..." ...