建立外來鍵

單列外來鍵

CREATE TABLE products (
product_no integer PRIMARY KEY,
name text,
);

#demo1
CREATE TABLE orders (
order_id integer PRIMARY KEY, 
product_no integer REFERENCES products (product_no) ON DELETE CASCADE/CASCADE,
);
#demo2 因為如果缺少列的列表，則被引用表的主鍵將被用作被引用列
CREATE TABLE orders (
order_id integer
 
 PRIMARY KEY, 
product_no integer REFERENCES products ON DELETE CASCADE/CASCADE,
);

#插入資料順序
insert into products(product_no,name) values(1,'add1'),(2,'add2'),(3,'add3');
insert into orders(order_id,product_no) values(1,1),(2,2),(3,3);
#刪除資料順序
delete from orders
delete from products

組合外來鍵

CREATE TABLE
 
 public.t1 (
a integer , 
b integer, 
c integer,
constraint pk_t1 PRIMARY KEY(a, b)
);

CREATE TABLE sc.t2 (
a integer ,
b integer,
c integer,
constraint pk_t2 PRIMARY KEY(c),
constraint fk_t2_a_b FOREIGN KEY (a, b) REFERENCES t1 (a, b)
);

CASCADE特性

CREATE TABLE products (
product_no integer ,
name 
 
text,
constraint pk_products PRIMARY KEY(product_no)
);
CREATE TABLE orders (
order_id integer, 
product_no integer ,
constraint pk_orders PRIMARY KEY(order_id),
constraint fk_orders_product_no FOREIGN KEY (product_no) REFERENCES products (product_no) ON DELETE CASCADE
);
insert into products(product_no,name) values(1,'add1'),(2,'add2'),(3,'add3');
insert into orders(order_id,product_no) values(1,1),(2,2),(3,3);
#CASCADE 這種型別的外來鍵，刪除被引用鍵的同時也會刪除引用的所有行
# 以下刪除操作將會刪出products和orders的相關行
delete from products where product_no in (1,2,3) 
select * from products;
select * from orders;

RESTRICT 特性

CREATE TABLE products (
product_no integer ,
name text,
constraint pk_products PRIMARY KEY(product_no)
);
CREATE TABLE orders (
order_id integer, 
product_no integer ,
constraint pk_orders PRIMARY KEY(order_id),
constraint fk_orders_product_no FOREIGN KEY (product_no) REFERENCES products (product_no) ON DELETE RESTRICT
);
insert into products(product_no,name) values(1,'add1'),(2,'add2'),(3,'add3');
insert into orders(order_id,product_no) values(1,1),(2,2),(3,3);
#RESTRICT 這種型別的外來鍵，不允許刪除被應用的行
#以下刪除操作將會失敗
delete from products where product_no in (1,2,3) 
select * from products;
select * from orders;

PSQL查詢外來鍵

建立多種外來鍵用於測試

CREATE TABLE public.t1 (
  t1a integer , 
  t1b integer, 
  t1c integer,
  constraint pk_t1 PRIMARY KEY(t1a, t1b)
);
CREATE TABLE dbo.t2 (
  t2a integer ,
  t2b integer,
  t2c integer,
  constraint pk_t2 PRIMARY KEY(t2c),
  constraint fk_t2_a_b FOREIGN KEY (t2a, t2b) REFERENCES t1 (t1a, t1b)
);
CREATE TABLE public.t3 (
  t3a integer , 
  t3b integer, 
  t3c integer,
  constraint pk_t3 PRIMARY KEY(t3a, t3b)
);
CREATE TABLE dbo.t4 (
  t4a integer ,
  t4b integer,
  t4c integer,
  constraint pk_t4 PRIMARY KEY(t4c),
  constraint fk_t4_t4a_t4b FOREIGN KEY (t4a, t4b) REFERENCES t3 (t3b,t3a )
);
CREATE TABLE public.t5 (
  t5a integer , 
  t5b integer unique, 
  t5c integer,
  constraint pk_t5 PRIMARY KEY(t5a)
);
CREATE TABLE dbo.t6 (
  t6a integer ,
  t6b integer,
  t6c integer,
  constraint pk_t6 PRIMARY KEY(t6c),
  constraint fk_t6_t6b FOREIGN KEY (t6b) REFERENCES t5 (t5b )
);

查詢外來鍵相關資訊

script1

--查詢外來鍵相關資訊包含drop add 指令碼
select *
    ,'alter table '||foreign_table||' drop constraint '||fk_name as DropScript
    ,'alter table '||foreign_table||' add constraint '||fk_name||' foreign key( ' ||fk_columns||')'||' references '||primary_table||'('||unique_columns||') on delete RESTRICT' as AddScript
from(
    select 
        foreign_table,fk_name,
        string_agg(t1.fk_column, ', ' order by fk_unique_column_position) as fk_columns,
        primary_table,unique_constraint_name,
        string_agg(t1.unique_column, ', ' order by fk_unique_column_position) as unique_columns
    from(
        select 
            cu1.table_schema||'.'||cu1.table_name as foreign_table,
            r.constraint_schema,r.constraint_name as fk_name,
            cu1.column_name as fk_column,cu1.ordinal_position as fk_unique_column_position,
            cu2.table_schema||'.'||cu2.table_name as primary_table,
            r.unique_constraint_schema,r.unique_constraint_name,
            cu2.column_name as unique_column
        from  information_schema.table_constraints tco
        join information_schema.referential_constraints r
            on tco.constraint_schema = r.constraint_schema and tco.constraint_name = r.constraint_name
        join information_schema.key_column_usage cu1
            on r.constraint_schema=cu1.constraint_schema and r.constraint_name=cu1.constraint_name
        join information_schema.key_column_usage cu2
            on r.unique_constraint_schema=cu2.constraint_schema and r.unique_constraint_name=cu2.constraint_name 
            and cu2.ordinal_position =cu1.position_in_unique_constraint
        where tco.constraint_type = 'FOREIGN KEY'    
    ) as t1
    group by foreign_table,fk_name,primary_table,unique_constraint_name
) as result 

script2

 --查詢外來鍵相關資訊 不包含
select kcu.table_schema || '.' ||kcu.table_name as foreign_table,
       '>-' as rel,
       rel_tco.table_schema || '.' || rel_tco.table_name as primary_table,
       string_agg(kcu.column_name, ', ') as fk_columns,
       kcu.constraint_name
from information_schema.table_constraints tco
join information_schema.key_column_usage kcu
          on tco.constraint_schema = kcu.constraint_schema
          and tco.constraint_name = kcu.constraint_name
join information_schema.referential_constraints rco
          on tco.constraint_schema = rco.constraint_schema
          and tco.constraint_name = rco.constraint_name
join information_schema.table_constraints rel_tco
          on rco.unique_constraint_schema = rel_tco.constraint_schema
          and rco.unique_constraint_name = rel_tco.constraint_name
where tco.constraint_type = 'FOREIGN KEY'
group by kcu.table_schema,
         kcu.table_name,
         rel_tco.table_name,
         rel_tco.table_schema,
         kcu.constraint_name
order by kcu.table_schema,
         kcu.table_name;