这篇文章主要介绍了Postgresql 查询表引用或被引用的外键操作，具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧
今天更新两个SQL。是用来查询PG中，主表被子表引用的外键，或子表引用了哪个主表的主键。
废话不多说，直接上实验！
CentOS 7 + PG 10
创建两个实验表，test01为主表，test02为子表，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
插入数据
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".
查询主表被哪个子表引用。如果结果为空，说明没有任何子表引用的该表。
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'; # 输入主表
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)
查询子表引用的哪个主表。如果结果为空，说明没有任何引用主表。
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'; # 输入子表
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)
