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  • Postgresql 查询表引用或被引用的外键操作
  • 2021/2/2 11:38:26
  • 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本教程网。如有错误或未考虑完全的地方,望不吝赐教。