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 1test=# insert into test01 values (2, 'b');INSERT 0 1test=# insert into test01 values (3, 'c');INSERT 0 1test=# insert into test02 values (1, 1, 'a');INSERT 0 1test=# insert into test02 values (2, 1, 'a');INSERT 0 1test=# insert into test02 values (3, 1, 'a');INSERT 0 1test=# insert into test02 values (4, 2, 'b');INSERT 0 1test=# insert into test02 values (5, 2, 'b');INSERT 0 1test=# 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=# SELECTtc.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_deferredFROMinformation_schema.table_constraints AS tcJOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_nameJOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_namewhere 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=# SELECTtc.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_deferredFROMinformation_schema.table_constraints AS tcJOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_nameJOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_nameWHERE 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。如有错误或未考虑完全的地方，望不吝赐教。