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。
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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
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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。
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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。
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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）
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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服务器之家。如有错误或未考虑完全的地方，望不吝赐教。
原文链接：https://blog.csdn.net/chuckchen1222/article/details/83312397
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