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__id
UNIQUE_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_name
UNIQUE_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