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)
补充：PostgreSQL 外键引用查询
根据一个表名，查询所有外键引用它的表，以及那些外键的列名
key_column_usage（系统列信息表），
pg_constraint（系统所有约束表）
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：
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。如有错误或未考虑完全的地方，望不吝赐教。
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