Mysql数据类型
Mysql数据类型
数值类型
整形
浮点型
字符类型
日期
时间
日期时间
枚举类型 enum set
Mysql内置时间函数的使用
使用时间函数获取数据给日期时间类型字段符值
Datetime与timetamp的区别
数值类型宽度数字字符类型宽度的区别
Ageint(2)
Namechar(2)
DBA-Day02
字段约束条件
修改表结构
Mysql健值
[root@host50~]# date +%y
mysql>select year(20171120);
+----------------+
|year(20171120) |
+----------------+
| 2017 |
+----------------+
1row in set (0.00 sec)
mysql>
Insertinto db1.t1 values($a,$w);
mysql>select now();
+---------------------+
|now() |
+---------------------+
|2018-06-15 09:24:56 |
+---------------------+
1row in set (0.00 sec)
mysql>
mysql>select year(now());
+-------------+
|year(now()) |
+-------------+
| 2018 |
+-------------+
1row in set (0.01 sec)
mysql>
mysql>select date(now());
+-------------+
|date(now()) |
+-------------+
|2018-06-15 |
+-------------+
1row in set (0.00 sec)
mysql>
mysql>select month(now());
+--------------+
|month(now()) |
+--------------+
| 6 |
+--------------+
1row in set (0.00 sec)
mysql>select time(now());
+-------------+
|time(now()) |
+-------------+
|09:26:34 |
+-------------+
1row in set (0.00 sec)
mysql>
mysql>select sleep(2);
+----------+
|sleep(2) |
+----------+
| 0 |
+----------+
1row in set (2.00 sec)
mysql>
mysql>select curdate();
+------------+
|curdate() |
+------------+
|2018-06-15 |
+------------+
1row in set (0.00 sec)
mysql>
mysql>desc t7;
+----------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
|name | char(15) | YES | | NULL | |
|syear | year(4) | YES | | NULL | |
|birthday | date | YES | | NULL | |
|up_class | time | YES | | NULL | |
|party | datetime | YES | | NULL | |
+----------+----------+------+-----+---------+-------+
5rows in set (0.00 sec)
mysql>insert into t7values("jing",year(19901120),date(now()),083000,now());
QueryOK, 1 row affected (0.32 sec)
mysql>select * from t7;
+------+-------+------------+----------+---------------------+
|name | syear | birthday | up_class | party |
+------+-------+------------+----------+---------------------+
|yaya | 1990 | 2018-11-20 | 08:30:00 | 2018-06-18 21:30:00 |
|yaya | 2053 | 2018-11-20 | 08:30:00 | 2018-11-18 21:30:00 |
|yaya | 1953 | 2018-11-20 | 08:30:00 | 2018-11-18 21:30:00 |
|jing | 1990 | 2018-06-15 | 08:30:00 | 2018-06-15 09:37:31 |
+------+-------+------------+----------+---------------------+
4rows in set (0.00 sec)
mysql>
mysql>create table t8(
->name char(5),
->meetting datetime,
->party timestamp);
QueryOK, 0 rows affected (0.21 sec)
mysql>insert into t8 values("bob",now(),now());
QueryOK, 1 row affected (0.09 sec)
mysql>select * from t8;
+------+---------------------+---------------------+
|name | meetting | party |
+------+---------------------+---------------------+
|bob | 2018-06-15 09:46:58 | 2018-06-15 09:46:58 |
+------+---------------------+---------------------+
1row in set (0.00 sec)
mysql>insert into t8(name,meetting) values("lucy",20191120214858);
QueryOK, 1 row affected (0.04 sec)
mysql>insert into t8(name,party) values("lucy",20151120214858);
QueryOK, 1 row affected (0.10 sec)
mysql>desc t8;
+----------+-----------+------+-----+-------------------+-----------------------------+
|Field | Type | Null | Key | Default | Extra |
+----------+-----------+------+-----+-------------------+-----------------------------+
|name | char(5) | YES | | NULL | |
|meetting | datetime | YES | | NULL | |
|party | timestamp | NO | | CURRENT_TIMESTAMP | on updateCURRENT_TIMESTAMP |
+----------+-----------+------+-----+-------------------+-----------------------------+
3rows in set (0.00 sec)
mysql>
mysql>select * from t8;
+------+---------------------+---------------------+
|name | meetting | party |
+------+---------------------+---------------------+
|bob | 2018-06-15 09:46:58 | 2018-06-15 09:46:58 |
|lucy | 2019-11-20 21:48:58 | 2018-06-15 09:51:55 |
|lucy | NULL | 2015-11-20 21:48:58 |
+------+---------------------+---------------------+
3rows in set (0.00 sec)
mysql>
数值类型宽度数字字符类型宽度的区别
mysql>create table t12(
->name char(5),
->level int(3) zerofill,
->money int(5) zerofill
->);
QueryOK, 0 rows affected (0.22 sec)
mysql>insert into t12 values("zbj",8,29);
QueryOK, 1 row affected (0.05 sec)
mysql>insert into t12 values("ts",888,2222229);
QueryOK, 1 row affected (0.04 sec)
mysql>insert into t12 values("fz",88888888,2222222229);
QueryOK, 1 row affected (0.04 sec)
mysql>select * from t12;
+------+----------+------------+
|name | level | money |
+------+----------+------------+
|swk | 018 | 00029 |
|zbj | 008 | 00029 |
|ts | 888 | 2222229 |
|fz | 88888888 | 2222222229 |
+------+----------+------------+
4rows in set (0.00 sec)
DBA-Day02
字段约束条件
修改表结构
MySQL键值
Field Type Null Key Default Extra
YES
Null:nullnot null
Default:0默认为null
mysql>insert into t12(name) values("bjm");
QueryOK, 1 row affected (0.05 sec)
mysql>select * from t12;
+------+----------+------------+
|name | level | money |
+------+----------+------------+
|swk | 018 | 00029 |
|zbj | 008 | 00029 |
|ts | 888 | 2222229 |
|fz | 88888888 | 2222222229 |
|bjm | NULL | NULL |
+------+----------+------------+
5rows in set (0.01 sec)
mysql>
mysql>create table t13( name char(5) not null, level int(3) zerofilldefault 0, money tinyint(2) zerofill default 0 );
额外设置
Extra i++
mysql>desc t13;
+-------+------------------------------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
|name | char(5) | NO | | NULL | |
|level | int(3) unsigned zerofill | YES | | 000 | |
|money | tinyint(2) unsigned zerofill | YES | | 00 | |
+-------+------------------------------+------+-----+---------+-------+
3rows in set (0.00 sec)
mysql>insert into t14(name) values("bob");
mysql>insert into t14 values(null,null,null);
ERROR1048 (23000): Column 'name' cannot be null
mysql>insert into t14 values("null",null,null);
QueryOK, 1 row affected (0.06 sec)
mysql>insert into t14 values ("",null,null);
QueryOK, 1 row affected (0.04 sec)
mysql>
mysql>create table t15( name char(5) not null default "", levelint(3) zerofill default 0, money tinyint(2) zerofill default 0 );
QueryOK, 0 rows affected (0.20 sec)
mysql>insert into t15 values();
QueryOK, 1 row affected (0.05 sec)
mysql>select * from t15;
+------+-------+-------+
|name | level | money |
+------+-------+-------+
| | 000 | 00 |
+------+-------+-------+
1row in set (0.00 sec)
mysql>
修改表结构
Altertable 表名 执行动作；
Add字段
mysql>Alter table t15 Add Email varchar(30) default "[email protected]",Add tel char(11);
mysql>select * from t15;
+------+-------+-------+-------------+------+
|name | level | money | Email | tel |
+------+-------+-------+-------------+------+
| | 000 | 00 | [email protected] | NULL |
+------+-------+-------+-------------+------+
1row in set (0.00 sec)
mysql>
Altertable t15
Addstu_id char(9) first;
mysql>Alter table t15
->Add stu_id char(9) first;
QueryOK, 0 rows affected (0.48 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>select * from t15;
+--------+------+-------+-------+-------------+------+
|stu_id | name | level | money | Email | tel |
+--------+------+-------+-------+-------------+------+
|NULL | | 000 | 00 | [email protected] | NULL |
+--------+------+-------+-------+-------------+------+
1row in set (0.00 sec)
mysql>
mysql>Alter table t15 Add sex enum("boy","gril","no")default "no" after name;
QueryOK, 0 rows affected (0.39 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>select * from t15;
+--------+------+------+-------+-------+-------------+------+
|stu_id | name | sex | level | money | Email | tel |
+--------+------+------+-------+-------+-------------+------+
|NULL | | no | 000 | 00 | [email protected] | NULL |
+--------+------+------+-------+-------+-------------+------+
1row in set (0.00 sec)
mysql>
mysql>alter table t15 modify stu_id varchar(10);
mysql>alter table t15 modify name char(10) not null;
mysql>alter table t15 modify tel char(11) after name;
QueryOK, 0 rows affected (0.43 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>desc t15;
+--------+------------------------------+------+-----+-------------+-------+
|Field | Type | Null | Key | Default |Extra |
+--------+------------------------------+------+-----+-------------+-------+
|stu_id | varchar(10) | YES | | NULL | |
|name | char(10) | NO | | NULL | |
|tel | char(11) | YES | | NULL | |
|sex | enum('boy','gril','no') | YES | | no | |
|level | int(3) unsigned zerofill | YES | | 000 | |
|money | tinyint(2) unsigned zerofill | YES | | 00 | |
|Email | varchar(30) | YES | | [email protected] | |
+--------+------------------------------+------+-----+-------------+-------+
7rows in set (0.00 sec)
mysql>
mysql>alter table t15 drop stu_id,drop tel;
QueryOK, 0 rows affected (0.41 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>
mysql>alter table t15
->change email mail varchar(30) default "[email protected]";
QueryOK, 0 rows affected (0.06 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>select * from t15;
+------+------+-------+-------+-------------+
|name | sex | level | money | mail |
+------+------+-------+-------+-------------+
| | no | 000 | 00 | [email protected] |
+------+------+-------+-------+-------------+
1row in set (0.00 sec)
mysql>
mysql>alter table t15 change mail Email varchar(50) default "[email protected]";
QueryOK, 0 rows affected (0.08 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>
mysql>desc t15;
+-------+------------------------------+------+-----+-------------+-------+
|Field | Type | Null | Key | Default |Extra |
+-------+------------------------------+------+-----+-------------+-------+
|name | char(10) | NO | | NULL | |
|sex | enum('boy','gril','no') | YES | | no | |
|level | int(3) unsigned zerofill | YES | | 000 | |
|money | tinyint(2) unsigned zerofill | YES | | 00 | |
|Email | varchar(50) | YES | | [email protected] | |
+-------+------------------------------+------+-----+-------------+-------+
5rows in set (0.00 sec)
mysql>
mysql>alter table t15 rename stuinfo;
QueryOK, 0 rows affected (0.10 sec)
mysql>show tables;
+---------------+
|Tables_in_db1 |
+---------------+
|stuinfo |
|t12 |
|t13 |
|t14 |
|t2 |
|t3 |
|t4 |
|t5 |
|t6 |
|t7 |
|t8 |
+---------------+
11rows in set (0.00 sec)
mysql>
[root@host50~]# cd /var/lib/mysql/db1
[root@host50db1]# ls *stuinfo
ls:无法访问*stuinfo:没有那个文件或目录
[root@host50db1]# ls
db.opt t12.frm t13.ibd t2.frm t3.ibd t5.frm t6.ibd t8.frm
stuinfo.frm t12.ibd t14.frm t2.ibd t4.frm t5.ibd t7.frm t8.ibd
stuinfo.ibd t13.frm t14.ibd t3.frm t4.ibd t6.frm t7.ibd
[root@host50db1]# ls stuinfo.*
stuinfo.frm stuinfo.ibd
[root@host50db1]#
Ctrl-
Ctrl+shift+
Descmysql.user;
Mysql键值
普通索引 index *
唯一索引 unique
主键 primary key *
外键 foreign key *
全文索引 fulltext
使用规则 创建 删除 查看
把常见的查询的字段作为索引
INDEX字段key的标志为MUL字段可以为空和重复
mysql>show index from t14;
Emptyset (0.00 sec)
mysql>
BTREE二叉树算法
1-10
1-5 6-10
1-2.5 2.6-5
Createtable t16(
Namechar(10),
Ageint(2),
Classchar(7),
Index(name),
Index(class)
);
Desct16;
mysql>desc t16;
+-------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
|Name | char(10) | YES | MUL | NULL | |
|Age | int(2) | YES | | NULL | |
|Class | char(7) | YES | MUL | NULL | |
+-------+----------+------+-----+---------+-------+
3rows in set (0.00 sec)
mysql>
Dropindex class on t16;
Showindex from t16\G;
mysql>Show index from t16\G;
***************************1. row ***************************
Table: t16
Non_unique: 1
Key_name: Name
Seq_in_index: 1
Column_name: Name
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
1row in set (0.00 sec)
ERROR:
Noquery specified
mysql>
mysql>desc stuinfo;
+-------+------------------------------+------+-----+-------------+-------+
|Field | Type | Null | Key | Default |Extra |
+-------+------------------------------+------+-----+-------------+-------+
|name | char(10) | NO | | NULL | |
|sex | enum('boy','gril','no') | YES | | no | |
|level | int(3) unsigned zerofill | YES | | 000 | |
|money | tinyint(2) unsigned zerofill | YES | | 00 | |
|Email | varchar(50) | YES | | [email protected] | |
+-------+------------------------------+------+-----+-------------+-------+
5rows in set (0.00 sec)
mysql>show index from stuinfo;
Emptyset (0.00 sec)
mysql>select * from stuinfo;
+------+------+-------+-------+-------------+
|name | sex | level | money | Email |
+------+------+-------+-------+-------------+
| | no | 000 | 00 | [email protected] |
+------+------+-------+-------+-------------+
1row in set (0.00 sec)
mysql>
mysql>create index name on stuinfo(name);
QueryOK, 0 rows affected (0.23 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>desc stuinfo;
+-------+------------------------------+------+-----+-------------+-------+
|Field | Type | Null | Key | Default |Extra |
+-------+------------------------------+------+-----+-------------+-------+
|name | char(10) | NO | MUL | NULL | |
|sex | enum('boy','gril','no') | YES | | no | |
|level | int(3) unsigned zerofill | YES | | 000 | |
|money | tinyint(2) unsigned zerofill | YES | | 00 | |
|Email | varchar(50) | YES | | [email protected] | |
+-------+------------------------------+------+-----+-------------+-------+
5rows in set (0.00 sec)
mysql>
mysql>create index xxxx on stuinfo(sex);
QueryOK, 0 rows affected (0.20 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>show index from stuinfo\G;
***************************1. row ***************************
Table: stuinfo
Non_unique: 1
Key_name: name
Seq_in_index: 1
Column_name: name
Collation: A
Cardinality: 1
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
***************************2. row ***************************
Table: stuinfo
Non_unique: 1
Key_name: xxxx
Seq_in_index: 1
Column_name: sex
Collation: A
Cardinality: 1
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
2rows in set (0.00 sec)
ERROR:
Noquery specified
mysql>
mysql>desc t16;
+-------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
|Name | char(10) | YES | MUL | NULL | |
|Age | int(2) | YES | | NULL | |
|Class | char(7) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
3rows in set (0.00 sec)
mysql>create index class on t16(class);
QueryOK, 0 rows affected (0.13 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>desc;
ERROR1064 (42000): You have an error in your SQL syntax; check the manualthat corresponds to your MySQL server version for the right syntax touse near '' at line 1
mysql>desc t16;
+-------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
|Name | char(10) | YES | MUL | NULL | |
|Age | int(2) | YES | | NULL | |
|Class | char(7) | YES | MUL | NULL | |
+-------+----------+------+-----+---------+-------+
3rows in set (0.00 sec)
mysql>
经常作为查询条件的字段作为索引 （默认可以为空值与重复，加快查询速度）
Primarykey主键（不能重复且不为空值）如：身份证号
一个表中只能有一个主键
如果有多个字段都作为主键称为复合主键
Createtable t17(
Stu_idchar(9) primary key,
Name char(10)
);
+--------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+--------+----------+------+-----+---------+-------+
|Stu_id | char(9) | NO | PRI | NULL | |
|Name | char(10) | YES | | NULL | |
+--------+----------+------+-----+---------+-------+
2rows in set (0.00 sec)
mysql>
mysql>insert into t17 values("nsd1803","bob");
QueryOK, 1 row affected (0.04 sec)
mysql>insert into t17 values("nsd1803","tom");
ERROR1062 (23000): Duplicate entry 'nsd1803' for key 'PRIMARY'
mysql>
mysql>insert into t17 values(null,"tom");
ERROR1048 (23000): Column 'Stu_id' cannot be null
mysql>
Createtable t18(
Stu_idchar(9) ,
Name char(10),
Primarykey(Stu_id)
);
mysql>alter table t17 drop primary key;
QueryOK, 2 rows affected (0.61 sec)
Records:2 Duplicates: 0 Warnings: 0
mysql>desc t17;
+--------+----------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+--------+----------+------+-----+---------+-------+
|Stu_id | char(9) | NO | | NULL | |
|Name | char(10) | YES | | NULL | |
+--------+----------+------+-----+---------+-------+
2rows in set (0.00 sec)
mysql>
altertable t17 add primary key(stu_id);
mysql>desc mysql.db;
+-----------------------+---------------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra|
+-----------------------+---------------+------+-----+---------+-------+
|Host | char(60) | NO | PRI | | |
|Db | char(64) | NO | PRI | | |
|User | char(32) | NO | PRI | | |
|Select_priv | enum('N','Y') | NO | | N | |
|Insert_priv | enum('N','Y') | NO | | N | |
|Update_priv | enum('N','Y') | NO | | N | |
|Delete_priv | enum('N','Y') | NO | | N | |
|Create_priv | enum('N','Y') | NO | | N | |
|Drop_priv | enum('N','Y') | NO | | N | |
|Grant_priv | enum('N','Y') | NO | | N | |
|References_priv | enum('N','Y') | NO | | N | |
|Index_priv | enum('N','Y') | NO | | N | |
|Alter_priv | enum('N','Y') | NO | | N | |
|Create_tmp_table_priv | enum('N','Y') | NO | | N | |
|Lock_tables_priv | enum('N','Y') | NO | | N | |
|Create_view_priv | enum('N','Y') | NO | | N | |
|Show_view_priv | enum('N','Y') | NO | | N | |
|Create_routine_priv | enum('N','Y') | NO | | N | |
|Alter_routine_priv | enum('N','Y') | NO | | N | |
|Execute_priv | enum('N','Y') | NO | | N | |
|Event_priv | enum('N','Y') | NO | | N | |
|Trigger_priv | enum('N','Y') | NO | | N | |
+-----------------------+---------------+------+-----+---------+-------+
22rows in set (0.00 sec)
mysql>
复合主键 (不能同时相同)
PRI PRI
cip serport status
1.1.1.1 22 no
1.1.1.1 21 yes
2.1.1.1 22 yes
create table t19(
cip char(15),
serport smallint(2),
status enum(“yes”,”no”),
primarykey(cip,serport)
);
复合主键要一起创建与SQL执行顺序有关
mysql>insert into t19 values("1.1.1.1",22,"no");
ERROR1062 (23000): Duplicate entry '1.1.1.1-22' for key 'PRIMARY'
mysql>insert into t19 values("1.1.1.1",22,"yes");
ERROR1062 (23000): Duplicate entry '1.1.1.1-22' for key 'PRIMARY'
mysql>insert into t19 values("1.1.1.1",21,"yes");
QueryOK, 1 row affected (0.03 sec)
mysql>insert into t19 values("1.1.1.2",21,"yes");
QueryOK, 1 row affected (0.05 sec)
mysql>
mysql>select * from t19;
+---------+---------+--------+
|cip | serport | status |
+---------+---------+--------+
|1.1.1.1 | 21 | yes |
|1.1.1.1 | 22 | no |
|1.1.1.2 | 21 | yes |
+---------+---------+--------+
3rows in set (0.00 sec)
mysql>
mysql>alter table t19 drop primary key(cip);
ERROR1064 (42000): You have an error in your SQL syntax; check the manualthat corresponds to your MySQL server version for the right syntax touse near '(cip)' at line 1
mysql>alter table t19 drop primary key;
QueryOK, 3 rows affected (0.68 sec)
Records:3 Duplicates: 0 Warnings: 0
mysql>
mysql>desc t19;
+---------+------------------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+---------+------------------+------+-----+---------+-------+
|cip | char(15) | NO | | NULL | |
|serport | smallint(2) | NO | | NULL | |
|status | enum('yes','no') | YES | | NULL | |
+---------+------------------+------+-----+---------+-------+
3rows in set (0.00 sec)
mysql>
mysql>insert into t19 values("1.1.1.1",22,"no");
QueryOK, 1 row affected (0.02 sec)
mysql>insert into t19 values("1.1.1.1",22,"no");
QueryOK, 1 row affected (0.07 sec)
mysql>insert into t19 values("1.1.1.1",null,"no");
ERROR1048 (23000): Column 'serport' cannot be null
mysql>
mysql>delete from t19;
QueryOK, 6 rows affected (0.06 sec)
mysql>select * from t19;
Emptyset (0.00 sec)
mysql>
mysql>alter table t19 add primary key(cip,serport);
QueryOK, 0 rows affected (0.58 sec)
Records:0 Duplicates: 0 Warnings: 0
mysql>desc t19;
+---------+------------------+------+-----+---------+-------+
|Field | Type | Null | Key | Default | Extra |
+---------+------------------+------+-----+---------+-------+
|cip | char(15) | NO | PRI | NULL | |
|serport | smallint(2) | NO | PRI | NULL | |
|status | enum('yes','no') | YES | | NULL | |
+---------+------------------+------+-----+---------+-------+
3rows in set (0.01 sec)
mysql>
AUTO_INCREMENT 字段的值自增长 ++ （必须是主键与数值类型）
createtable t20(
stu_idint(2) primary key
auto_increment,
namechar(10),
agetinyint(2)
);
mysql>desc t20;
+--------+------------+------+-----+---------+----------------+
|Field | Type | Null | Key | Default | Extra |
+--------+------------+------+-----+---------+----------------+
|stu_id | int(2) | NO | PRI | NULL | auto_increment |
|name | char(10) | YES | | NULL | |
|age | tinyint(2) | YES | | NULL | |
+--------+------------+------+-----+---------+----------------+
3rows in set (0.00 sec)
mysql>
mysql>insert into t20(name,age) values("bob",19);
QueryOK, 1 row affected (0.30 sec)
mysql>
mysql>insert into t20(name,age) values("lucy",19);
QueryOK, 1 row affected (0.04 sec)
mysql>insert into t20(name,age) values("jerryy",19);
QueryOK, 1 row affected (0.04 sec)
mysql>select * from t20;
+--------+--------+------+
|stu_id | name | age |
+--------+--------+------+
| 1 | bob | 19 |
| 2 | lucy | 19 |
| 3 | jerryy | 19 |
+--------+--------+------+
3rows in set (0.00 sec)
mysql>
mysql>insert into t20 values(1,"jerryy",19);
ERROR1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql>insert into t20 values(null,"jerryy",19);
QueryOK, 1 row affected (0.06 sec)
mysql>
mysql>select * from t20;
+--------+--------+------+
|stu_id | name | age |
+--------+--------+------+
| 1 | bob | 19 |
| 2 | lucy | 19 |
| 3 | jerryy | 19 |
| 4 | jerryy | 19 |
+--------+--------+------+
4rows in set (0.00 sec)
mysql>
mysql>insert into t20(name,age) values("jack",19);
QueryOK, 1 row affected (0.04 sec)
mysql>
经常把行号字段设置为主键
mysql>select * from stuinfo;
+------+------+-------+-------+-------------+
|name | sex | level | money | Email |
+------+------+-------+-------+-------------+
| | no | 000 | 00 | [email protected] |
+------+------+-------+-------+-------------+
1row in set (0.00 sec)
mysql>alter table stuinfo
-> add
-> id int(2)primary key auto_increment
-> first;
QueryOK, 0 rows affected (0.52 sec)
Records:0 Duplicates: 0 Warnings: 0