一、表介绍
表相当于文件,表中的一条记录就相当于文件的一行内容,不同的是,表中的一条记录有对应的标题,称为表的字段。
id,name,age,sex称为字段,其余的,一行内容称为一条记录
二、创建表
1,语法:
# 语法: create table 表名( 字段名1 类型[(宽度) 约束条件], 字段名2 类型[(宽度) 约束条件], 字段名3 类型[(宽度) 约束条件] ); # 注意: 1. 在同一张表中,字段名是不能相同 2. 宽度和约束条件可选 3. 字段名和类型是必须的
2,示范:
mysql> create database db1 charset utf8; Query OK, 1 row affected, 1 warning (0.11 sec) mysql> use db1; Database changed mysql> mysql> create table t1( -> id int, -> name varchar(50), -> sex enum('male','female'), -> age int(3) -> ); Query OK, 0 rows affected, 1 warning (0.63 sec) mysql> show tables; # 查看 db1 库下的所有表名 +---------------+ | Tables_in_db1 | +---------------+ | t1 | +---------------+ 1 row in set (0.00 sec) mysql> desc t1; # 这个更清晰 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.07 sec) mysql> select id,name,sex,age from t1; Empty set (0.00 sec) mysql> select * from t1; Empty set (0.00 sec) mysql> select id,name from t1; Empty set (0.00 sec) mysql>
3,往表中插入数据
mysql> insert into t1 values -> (1,'zixi','male',18), -> (2,'suosuo','male',20) -> ; Query OK, 2 rows affected (0.10 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> insert into t1(id) values -> (3), -> (4); Query OK, 2 rows affected (0.07 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> select * from t1; +------+--------+------+------+ | id | name | sex | age | +------+--------+------+------+ | 1 | zixi | male | 18 | | 2 | suosuo | male | 20 | | 3 | NULL | NULL | NULL | | 4 | NULL | NULL | NULL | +------+--------+------+------+ 4 rows in set (0.00 sec) mysql>
!!!注意!!!:表中的最后一个字段不要加逗号
三、查看表结构
如下:
mysql> describe t1; # 查看表结构,可简写为 desc 表名 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> show create table t1G # 查看表详细结构,可加G *************************** 1. row *************************** Table: t1 Create Table: CREATE TABLE `t1` ( `id` int DEFAULT NULL, `name` varchar(50) DEFAULT NULL, `sex` enum('male','female') DEFAULT NULL, `age` int DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8 1 row in set (0.00 sec) mysql>
四、修改表结构
1,语法:
语法: 1. 修改表名 ALTER TABLE 表名 RENAME 新表名; 2. 增加字段 ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…], ADD 字段名 数据类型 [完整性约束条件…]; ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…] FIRST; ALTER TABLE 表名 ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名; 3. 删除字段 ALTER TABLE 表名 DROP 字段名; 4. 修改字段 ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…]; ALTER TABLE 表名 CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…]; ALTER TABLE 表名 CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];
2,示例:
1. 修改存储引擎 mysql> alter table service -> engine=innodb; 2. 添加字段 mysql> alter table student10 -> add name varchar(20) not null, -> add age int(3) not null default 22; mysql> alter table student10 -> add stu_num varchar(10) not null after name; //添加name字段之后 mysql> alter table student10 -> add sex enum('male','female') default 'male' first; //添加到最前面 3. 删除字段 mysql> alter table student10 -> drop sex; mysql> alter table service -> drop mac; 4. 修改字段类型modify mysql> alter table student10 -> modify age int(3); mysql> alter table student10 -> modify id int(11) not null primary key auto_increment; //修改为主键 5. 增加约束(针对已有的主键增加auto_increment) mysql> alter table student10 modify id int(11) not null primary key auto_increment; ERROR 1068 (42000): Multiple primary key defined mysql> alter table student10 modify id int(11) not null auto_increment; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 6. 对已经存在的表增加复合主键 mysql> alter table service2 -> add primary key(host_ip,port); 7. 增加主键 mysql> alter table student1 -> modify name varchar(10) not null primary key; 8. 增加主键和自动增长 mysql> alter table student1 -> modify id int not null primary key auto_increment; 9. 删除主键 a. 删除自增约束 mysql> alter table student10 modify id int(11) not null; b. 删除主键 mysql> alter table student10 -> drop primary key;
五、复制表
如下:
1,复制表结构 + 记录(key不会复制:主键,外键和索引)
mysql> use db1; Database changed mysql> show tables; +---------------+ | Tables_in_db1 | +---------------+ | t1 | +---------------+ 1 row in set (0.00 sec) mysql> desc t1; # 看表结构 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> select * from t1; # 看记录 +------+--------+------+------+ | id | name | sex | age | +------+--------+------+------+ | 1 | zixi | male | 18 | | 2 | suosuo | male | 20 | | 3 | NULL | NULL | NULL | | 4 | NULL | NULL | NULL | +------+--------+------+------+ 4 rows in set (0.00 sec) mysql> create table t2 select * from t1; # 复制表结构和记录给t2 Query OK, 4 rows affected (0.48 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql> desc t2; # 查看 t2 的表结构 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> select * from t2; # 查看 t2 的记录,和 t1 的是一样的 +------+--------+------+------+ | id | name | sex | age | +------+--------+------+------+ | 1 | zixi | male | 18 | | 2 | suosuo | male | 20 | | 3 | NULL | NULL | NULL | | 4 | NULL | NULL | NULL | +------+--------+------+------+ 4 rows in set (0.00 sec) mysql>
2,只拷贝表结构,不要记录(方法一:)
mysql> select * from t1 where 1>5; # 这个条件为假,查不出结果,但是有表结构。 Empty set (0.04 sec) mysql> create table t3 select * from t1 where 1>5; # 复制表 Query OK, 0 rows affected (0.38 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t3; # 查看表结构 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> select * from t3; # 只复制了表结构,所以记录为空 Empty set (0.00 sec) mysql>
3,只拷贝表结构,不要记录(方法二:)
mysql> create table t4 like t1; # 只拷贝 t1 的表结构 Query OK, 0 rows affected (0.62 sec) mysql> desc t4; # t4 的表结构与 t1是一样的 +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | id | int | YES | | NULL | | | name | varchar(50) | YES | | NULL | | | sex | enum('male','female') | YES | | NULL | | | age | int | YES | | NULL | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) mysql> select * from t4; # 记录是没有的 Empty set (0.00 sec) mysql>
六、删除表
如下:
DROP TABLE 表名;