From ce2f8630e74667a5c97238c397208cd2926c9241 Mon Sep 17 00:00:00 2001
From: yangj1211 <153493538+yangj1211@users.noreply.github.com>
Date: Mon, 6 May 2024 14:09:46 +0800
Subject: [PATCH] Foreign key checks (#1045)

* add doc of foreign_key_checks

* add doc of foreign_key_checks
---
 .../data-integrity/foreign-key-constraints.md |   2 +
 .../system-variables/foreign_key_checks.md    | 100 ++++++++++++++++++
 mkdocs.yml                                    |   1 +
 3 files changed, 103 insertions(+)
 create mode 100644 docs/MatrixOne/Reference/Variable/system-variables/foreign_key_checks.md

diff --git a/docs/MatrixOne/Develop/schema-design/data-integrity/foreign-key-constraints.md b/docs/MatrixOne/Develop/schema-design/data-integrity/foreign-key-constraints.md
index 0a4c38a390..eb1b7fddf0 100644
--- a/docs/MatrixOne/Develop/schema-design/data-integrity/foreign-key-constraints.md
+++ b/docs/MatrixOne/Develop/schema-design/data-integrity/foreign-key-constraints.md
@@ -2,6 +2,8 @@
 
 FOREIGN KEY 外键约束允许表内或跨表交叉引用相关数据，有助于保持相关数据的一致性。
 
+当建立外键时，Matrixone 默认会检查外键约束的完整性。如需禁用外键约束检查，请参考章节[外键约束检查](../../../Reference/Variable/system-variables/foreign_key_checks.md)。
+
 **遵循规则**
 
 定义外键时，需要遵守下列规则：
diff --git a/docs/MatrixOne/Reference/Variable/system-variables/foreign_key_checks.md b/docs/MatrixOne/Reference/Variable/system-variables/foreign_key_checks.md
new file mode 100644
index 0000000000..86449af10c
--- /dev/null
+++ b/docs/MatrixOne/Reference/Variable/system-variables/foreign_key_checks.md
@@ -0,0 +1,100 @@
+# 外键约束检查
+
+在 MatrixOne 中，`foreign_key_checks` 是一个系统变量，用于控制外键约束的检查。这个变量可以是全局的，也可以是会话级别的。当设置为 1（默认值）时，MatrixOne 会检查外键约束的完整性，确保数据的参照完整性。如果设置为 0，则跳过这些检查。
+
+!!! note
+    与 MySQL 行为不一致的是，当关闭外键约束检查时，删除父表，MySQL 不会删除子表引用父表的外键关系，但 MatrixOne 会删除子表引用父表的外键关系，重建父表后会重新建立外键关系。
+
+## 查看 foreign_key_checks
+
+在 MatrixOne 中使用以下命令查看 foreign_key_checks：
+
+```sql
+
+--全局模式
+SELECT @@global.foreign_key_checks;
+SHOW global VARIABLES LIKE 'foreign_key_checks';
+
+--会话模式
+SELECT @@session.foreign_key_checks;
+SHOW session VARIABLES LIKE 'foreign_key_checks';
+```
+
+## 设置 foreign_key_checks
+
+在 MatrixOne 中使用以下命令设置 foreign_key_checks：
+
+```sql
+--全局模式，重新连接数据库生效
+set global foreign_key_checks = 'xxx' 
+
+--会话模式
+set session foreign_key_checks = 'xxx'
+```
+
+## 示例
+
+```sql
+mysql>  SELECT @@session.foreign_key_checks;
++----------------------+
+| @@foreign_key_checks |
++----------------------+
+| 1                    |
++----------------------+
+1 row in set (0.00 sec)
+
+create table t2(a int primary key,b int);
+create table t1( b int, constraint `c1` foreign key `fk1` (b) references t2(a));
+
+insert into t2 values(1,2);
+mysql> insert into t1 values(3);--开启外键约束检查时，不能插入违反约束的值
+ERROR 20101 (HY000): internal error: Cannot add or update a child row: a foreign key constraint fails
+
+mysql> drop table t2;--开启外键约束检查时，不能删除父表
+ERROR 20101 (HY000): internal error: can not drop table 't2' referenced by some foreign key constraint
+
+set session foreign_key_checks =0;--关闭外键约束检查
+mysql>  SELECT @@session.foreign_key_checks;
++----------------------+
+| @@foreign_key_checks |
++----------------------+
+| 0                    |
++----------------------+
+1 row in set (0.00 sec)
+
+mysql> insert into t1 values(3);--关闭外键约束检查时，可以插入违反约束的值
+Query OK, 1 row affected (0.01 sec)
+
+mysql> drop table t2;--关闭外键约束检查时，可以删除父表，
+Query OK, 0 rows affected (0.02 sec)
+
+mysql> show create table t1;--删除父表，外键约束也被删除
++-------+--------------------------------------------+
+| Table | Create Table                               |
++-------+--------------------------------------------+
+| t1    | CREATE TABLE `t1` (
+`b` INT DEFAULT NULL
+) |
++-------+--------------------------------------------+
+1 row in set (0.00 sec)
+
+mysql> create table t2(n1 int);--重建被删除的父表 t2，需包含子表原外键引用列
+ERROR 20101 (HY000): internal error: column 'a' no exists in table ''
+
+mysql> create table t2(n1 int,a int primary key);--包含被引用的主键列 a，重建成功
+Query OK, 0 rows affected (0.01 sec)
+
+mysql> show create table t1;--重建 t2 后，外键关系会自动重新建立
++-------+-------------------------------------------------------------------------------------------------------------------------------------------+
+| Table | Create Table                                                                                                                              |
++-------+-------------------------------------------------------------------------------------------------------------------------------------------+
+| t1    | CREATE TABLE `t1` (
+`b` INT DEFAULT NULL,
+CONSTRAINT `c1` FOREIGN KEY (`b`) REFERENCES `t2` (`a`) ON DELETE RESTRICT ON UPDATE RESTRICT
+) |
++-------+-------------------------------------------------------------------------------------------------------------------------------------------+
+1 row in set (0.00 sec)
+
+
+
+```
diff --git a/mkdocs.yml b/mkdocs.yml
index 552b4c5872..731738d686 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -256,6 +256,7 @@ nav:
           - 保存查询结果支持: MatrixOne/Reference/Variable/system-variables/save_query_result.md
           - 时区支持: MatrixOne/Reference/Variable/system-variables/timezone.md
           - 大小写敏感支持: MatrixOne/Reference/Variable/system-variables/lower_case_tables_name.md
+          - 外键检查支持: MatrixOne/Reference/Variable/system-variables/foreign_key_checks.md
         - 自定义变量: MatrixOne/Reference/Variable/custom-variable.md
       - SQL 结构与语法:
         - 关键字: MatrixOne/Reference/Language-Structure/keywords.md