MySQL 8.0新特性 — 检查性约束的使用简介

吾爱主题阅读：160 2024-04-02 08:00:48 评论：0

前言

在mysql 8.0版本中，引入了一个非常有用的新特性 — 检查性约束，它可以提高对非法或不合理数据写入的控制能力；接下来我们就来详细了解一下。

检查性约束

创建、删除与查看

（1）可以在建表时，创建检查性约束

1 2 3 4 5 6 7 8 9 10 mysql> create table t1 -> ( -> check (c1 <> c2), -> c1 int check (c1 > 10), -> c2 int constraint c2_positive check (c2 > 0), -> c3 int check (c3 < 100), -> constraint c1_nonzero check (c1 <> 0), -> check (c1 > c3) -> ); query ok, 0 rows affected (0.03 sec)

（2）也可以通过下列语句，新增检查性约束

1 2 3 mysql> alter table t1 add constraint c3_nonzero check ((c3<>0)); query ok, 0 rows affected (0.16 sec) records: 0 duplicates: 0 warnings: 0

（3）可以通过下列语句，删除检查性约束

1 2 3 mysql> alter table t1 drop constraint c3_nonzero; query ok, 0 rows affected (0.02 sec) records: 0 duplicates: 0 warnings: 0

（4）可以通过查询表结构的方式，查看检查性约束

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 mysql> show create table t1\g *************************** 1. row *************************** table : t1 create table : create table `t1` ( `c1` int default null , `c2` int default null , `c3` int default null , constraint `c1_nonzero` check ((`c1` <> 0)), constraint `c2_positive` check ((`c2` > 0)), constraint `t1_chk_1` check ((`c1` <> `c2`)), constraint `t1_chk_2` check ((`c1` > 10)), constraint `t1_chk_3` check ((`c3` < 100)), constraint `t1_chk_4` check ((`c1` > `c3`)) ) engine=innodb default charset=utf8mb4 collate =utf8mb4_0900_ai_ci 1 row in set (0.00 sec)

（5）也可以通过下面两个视图查看，其中table_constraints查询表存在哪些约束，check_constraints查询检查性约束的具体定义

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 mysql> select * from information_schema.table_constraints where table_name= 't1' ; + --------------------+-------------------+-----------------+--------------+------------+-----------------+----------+ | constraint_catalog | constraint_schema | constraint_name | table_schema | table_name | constraint_type | enforced | + --------------------+-------------------+-----------------+--------------+------------+-----------------+----------+ | def | test | c1_nonzero | test | t1 | check | yes | | def | test | c2_positive | test | t1 | check | yes | | def | test | t1_chk_1 | test | t1 | check | yes | | def | test | t1_chk_2 | test | t1 | check | yes | | def | test | t1_chk_3 | test | t1 | check | yes | | def | test | t1_chk_4 | test | t1 | check | yes | + --------------------+-------------------+-----------------+--------------+------------+-----------------+----------+ 6 rows in set (0.00 sec) mysql> select * from information_schema.check_constraints where constraint_name= 'c1_nonzero' ; + --------------------+-------------------+-----------------+--------------+ | constraint_catalog | constraint_schema | constraint_name | check_clause | + --------------------+-------------------+-----------------+--------------+ | def | test | c1_nonzero | (`c1` <> 0) | + --------------------+-------------------+-----------------+--------------+ 1 row in set (0.00 sec)