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  • mysql --默认约束

    -----默认约束
    -----就是当我们插入字段值的时候,没有传值,就会使用默认值

    mysql> create table user10(
    -> id int,
    -> name varchar(20),
    -> age int default 10
    -> );
    Query OK, 0 rows affected (0.08 sec)

    mysql> desc user10;
    +-------+-------------+------+-----+---------+-------+
    | Field | Type | Null | Key | Default | Extra |
    +-------+-------------+------+-----+---------+-------+
    | id | int | YES | | NULL | |
    | name | varchar(20) | YES | | NULL | |
    | age | int | YES | | 10 | |
    +-------+-------------+------+-----+---------+-------+
    3 rows in set (0.03 sec)

    mysql>

    mysql> insert into user10 (id,name) values (1,"zhangsan");
    Query OK, 1 row affected (0.01 sec)

    mysql> select * from user10;
    +------+----------+------+
    | id | name | age |
    +------+----------+------+
    | 1 | zhangsan | 10 |
    +------+----------+------+
    1 row in set (0.00 sec)

    mysql>

    mysql> insert into user10 values(2,"lisi",18);
    Query OK, 1 row affected (0.00 sec)

    mysql> select * from user10;
    +------+----------+------+
    | id | name | age |
    +------+----------+------+
    | 1 | zhangsan | 10 |
    | 2 | lisi | 18 |
    +------+----------+------+
    2 rows in set (0.00 sec)

    mysql>

    ---传了值,就不会使用默认值。

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  • 原文地址:https://www.cnblogs.com/clairedandan/p/13283501.html
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