MySql 主鍵自動增長

2021-08-31 08:22:45 字數 2795 閱讀 9016

建立資料庫,建立表。

mysql> create database ssh2;

query ok, 1 row affected (0.04 sec)

mysql> use ssh2;

database changed

mysql> create table user(

-> id integer primary key,

-> firstname varchar(200) not null,

-> lastname varchar(200) not null,

-> age integer

-> );

query ok, 0 rows affected (0.46 sec)

給主鍵增加乙個自增的功能:

mysql> alter table user modify id integer auto_increment ;

query ok, 1 row affected (0.28 sec)

records: 1 duplicates: 0 warnings: 0

這樣,上面的user表裡面的主鍵,id可以自增了。

給上面的主鍵id增加預設值和自增功能。

mysql> alter table user modify id integer auto_increment ;

query ok, 0 rows affected (0.39 sec)

records: 0 duplicates: 0 warnings: 0

mysql> alter table user modify id integer default '1';

query ok, 0 rows affected (0.16 sec)

records: 0 duplicates: 0 warnings: 0

mysql> alter table user modify id integer auto_increment ;

query ok, 1 row affected (0.28 sec)

records: 1 duplicates: 0 warnings: 0

mysql> alter table user add createtime timestamp default current_timestamp;

query ok, 2 rows affected (0.17 sec)

records: 2 duplicates: 0 warnings: 0

mysql設定主鍵不能為空,還要自動增長(這裡沒有設定預設值,但是預設是1,從1開始增長。),還要得到系統預設日期:

mysql> create table dd(

-> id int primary key not null auto_increment,

-> name varchar(20),

-> time timestamp default current_timestamp

-> );

query ok, 0 rows affected (0.10 sec)

mysql> insert into dd(name) values ('fhihgifds');

query ok, 1 row affected (0.14 sec)

mysql> insert into dd(name) values ('steven');

query ok, 1 row affected (0.08 sec)

mysql> select * from dd;

+----+-----------+---------------------+

| id | name | time |

+----+-----------+---------------------+

| 1 | fhihgifds | 2011-03-27 01:58:46 |

| 2 | steven | 2011-03-27 01:59:35 |

+----+-----------+---------------------+

2 rows in set (0.08 sec)

mysql> insert into dd(name) values ('anthony');

query ok, 1 row affected (0.09 sec)

mysql> select * from dd;

+----+-----------+---------------------+

| id | name | time |

+----+-----------+---------------------+

| 1 | fhihgifds | 2011-03-27 01:58:46 |

| 2 | steven | 2011-03-27 01:59:35 |

| 3 | anthony | 2011-03-27 02:00:07 |

+----+-----------+---------------------+

3 rows in set (0.00 sec)

mysql>

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