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__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