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這篇文章主要介紹了Postgresql 查詢表引用或被引用的外鍵操作，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過(guò)來(lái)看看吧

今天更新兩個(gè)SQL。是用來(lái)查詢PG中，主表被子表引用的外鍵，或子表引用了哪個(gè)主表的主鍵。

廢話不多說(shuō)，直接上實(shí)驗(yàn)！

CentOS 7 + PG 10

創(chuàng)建兩個(gè)實(shí)驗(yàn)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

插入數(shù)據(jù)

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(gè)子表引用。如果結(jié)果為空，說(shuō)明沒(méi)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(gè)主表。如果結(jié)果為空，說(shuō)明沒(méi)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)

補(bǔ)充：PostgreSQL 外鍵引用查詢

根據(jù)一個(gè)表名，查詢所有外鍵引用它的表，以及那些外鍵的列名

key_column_usage（系統(tǒng)列信息表），

pg_constraint（系統(tǒng)所有約束表）

SELECT x.table_name,
    x.column_name
 FROM information_schema.key_column_usage x
 INNER JOIN (SELECT t.relname,
            a.conname
         FROM pg_constraint a
         INNER JOIN pg_class ft
             ON ft.oid = a.confrelid
         INNER JOIN pg_class t
             ON t.oid = a.conrelid
        WHERE a.contype = 'f'
         AND a.confrelid =
            (select e.oid
             from pg_class e
             where e.relname = 'xxx_table')
        ) tp
     ON (x.table_name = tp.relname AND
       x.constraint_name = tp.conname)

示例：

文章來(lái)源：腳本之家

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