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information_schema.referential_constraints 学习
information_schema.referential_constraints 表用于查看外键约束
1、information_schema.referential_constraints表的常用列：
1、constraint_schema ：约束(外键)所在的库名
2、constraint_name ：约束名(外键名)
3、unique_constraint_schema ：被引用约束所在库名
4、unique_constraint_name ：被引用约束名
2、例子：
1、定义一对有外键约束的表：
create table teacher(id int not null auto_increment,name varchar(4),constraint pk__teacher primary key(id),constraint ix__teacher__name unique index (name))engine=innodb default char set utf8;create table student(id int not null auto_increment,name varchar(4),teacher_id int not null,teacher_name varchar(4),constraint pk__student primary key(id),constraint fk__student__id foreign key (teacher_id ) references teacher(id),constraint fk__student__teacher_name foreign key (teacher_name) references teacher(name) on delete no action on update cascade)engine=innodb default char set utf8;
2、查看外键约束
select * from information_schema.referential_constraints \G*************************** 1. row *************************** CONSTRAINT_CATALOG: def CONSTRAINT_SCHEMA: tempdb CONSTRAINT_NAME: fk__student__idUNIQUE_CONSTRAINT_CATALOG: def UNIQUE_CONSTRAINT_SCHEMA: tempdb UNIQUE_CONSTRAINT_NAME: PRIMARY MATCH_OPTION: NONE UPDATE_RULE: RESTRICT DELETE_RULE: RESTRICT TABLE_NAME: student REFERENCED_TABLE_NAME: teacher*************************** 2. row *************************** CONSTRAINT_CATALOG: def CONSTRAINT_SCHEMA: tempdb CONSTRAINT_NAME: fk__student__teacher_nameUNIQUE_CONSTRAINT_CATALOG: def UNIQUE_CONSTRAINT_SCHEMA: tempdb UNIQUE_CONSTRAINT_NAME: ix__teacher__name MATCH_OPTION: NONE UPDATE_RULE: CASCADE DELETE_RULE: NO ACTION TABLE_NAME: student REFERENCED_TABLE_NAME: teacher
information_schema.referential_constraints 学习
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