今天更新兩個SQL。是用來查詢PG中，主表被子表引用的外來鍵，或子表引用了哪個主表的主鍵。

廢話不多說，直接上實驗！

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CentOS 7 + PG 10

建立兩個實驗表，test01為主表，test02為子表，test02引用test01中的id列。

test=# create table test01(

test(# id int primary key,

test(# col1 varchar(20)

test(# );

CREATE TABLE

test=# create table test02(

test(# id int primary key,

test(# test01_id int references test01(id),

test(# col1 varchar(20)

test(# );

CREATE TABLE

插入資料

test=# insert into test01 values (1, 'a');

INSERT 0 1

test=# insert into test01 values (2, 'b');

INSERT 0 1

test=# insert into test01 values (3, 'c');

INSERT 0 1

test=# insert into test02 values (1, 1, 'a');

INSERT 0 1

test=# insert into test02 values (2, 1, 'a');

INSERT 0 1

test=# insert into test02 values (3, 1, 'a');

INSERT 0 1

test=# insert into test02 values (4, 2, 'b');

INSERT 0 1

test=# insert into test02 values (5, 2, 'b');

INSERT 0 1

test=# insert into test02 values (6, 11, 'b');

ERROR: insert or update on table "test02" violates foreign key constraint "test02_test01_id_fkey"

DETAIL: Key (test01_id)=(11) is not present in table "test01".

查詢主表被哪個子表引用。如果結果為空，說明沒有任何子表引用的該表。

test=# SELECT

tc.constraint_name,

tc.table_name, # 子表

kcu.column_name,

ccu.table_name AS foreign_table_name, # 主表

ccu.column_name AS foreign_column_name,

tc.is_deferrable,

tc.initially_deferred

FROM

information_schema.table_constraints AS tc

JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name

JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name

where constraint_type = 'FOREIGN KEY' AND ccu.table_name='test01'; # 輸入主表

constraint_name | table_name | column_name | foreign_table_name | foreign_column_name | is_deferrable | initially_deferred

-----------------------+------------+-------------+--------------------+---------------------+---------------+--------------------

test02_test01_id_fkey | test02 | test01_id | test01 | id | NO | NO

(1 row)

查詢子表引用的哪個主表。如果結果為空，說明沒有任何引用主表。

test=# SELECT

tc.constraint_name,

tc.table_name, # 子表

kcu.column_name,

ccu.table_name AS foreign_table_name,

ccu.column_name AS foreign_column_name, # 主表

tc.is_deferrable,

tc.initially_deferred

FROM

information_schema.table_constraints AS tc

JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name

JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name

WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='test02'; # 輸入子表

constraint_name | table_name | column_name | foreign_table_name | foreign_column_name | is_deferrable | initially_deferred

-----------------------+------------+-------------+--------------------+---------------------+---------------+--------------------

test02_test01_id_fkey | test02 | test01_id | test01 | id | NO | NO

(1 row)