Find table relations from SQL Server - sql

Question

I would like to know how to discover which tables are related each other in my SQL Server database by running a SQL query.
As example, suppose I have 2 many-to-many relations and 3 tables initialized with some random values.
create table A (pk int not null primary key identity, A int);
create table B (pk int not null primary key identity, B int);
create table C (pk int not null primary key identity, C int);
create table AB
(
a_pk int not null references A,
b_pk int not null references B,
primary key(a_pk, b_pk)
);
create table AC
(
a_pk int not null references A,
c_pk int not null references C,
primary key(a_pk, c_pk)
);
I would like to run a parametrized query having as output something like:
With parameter 'A':
MM_TAB | REL_TAB
------------------
AB | B
AC | C
With parameter 'B':
MM_TAB | REL_TAB
------------------
AB | A
With parameter 'C':
MM_TAB | REL_TAB
------------------
AC | A
How can I do that?

Answer 1

Check this out:
I created the tables and relations using SQL Server 2014:
create database relation
use relation
create table A (pk int not null primary key identity, A int);
create table B (pk int not null primary key identity, B int);
create table C (pk int not null primary key identity, C int);
create table AB
(
a_pk int not null foreign key references A(pk),
b_pk int not null foreign key references B(pk),
primary key(a_pk, b_pk)
);
create table AC
(
a_pk int not null foreign key references A(pk),
c_pk int not null foreign key references C(pk),
primary key(a_pk, c_pk)
);
Then you can use this query to find the related tables:
use relation
go
DECLARE #table_param NVARCHAR(2)='A';
with rel as(
SELECT
K_Table = FK.TABLE_NAME,
--FK_Column = CU.COLUMN_NAME,
PK_Table = PK.TABLE_NAME
--PK_Column = PT.COLUMN_NAME,
--Constraint_Name = C.CONSTRAINT_NAME
FROM
INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
INNER JOIN
INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME
INNER JOIN
INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME
INNER JOIN
INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU ON C.CONSTRAINT_NAME = CU.CONSTRAINT_NAME
wHERE PK.TABLE_NAME = #table_param
)
SELECT
K_Table = FK.TABLE_NAME,
--FK_Column = CU.COLUMN_NAME,
PK_Table = PK.TABLE_NAME
--PK_Column = PT.COLUMN_NAME,
--Constraint_Name = C.CONSTRAINT_NAME
FROM
INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
INNER JOIN
INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME
INNER JOIN
INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME
INNER JOIN
INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU ON C.CONSTRAINT_NAME = CU.CONSTRAINT_NAME
WHERE FK.TABLE_NAME IN(SELECT R.K_Table FROM REL R)