Delete unrelated records in one of some related tables - sql

Question

There is a table MainTable with a column MyField. There are some tables related by foreign keys to MainTable. Their names are unknown.
I need:
to find and delete all rows in MainTable which have no relation to any other table
query should return all MyField values of these deleted rows
Or as an option: query should return all MyField values for rows which are to be deleted.
Thanks!
UpDate1
Sorry I forgot to say I use Sql Server 2005.
MainTable has PK.
Other tables have FK.
Example
create table MainTable
(
ID int IDENTITY primary key,
MyField nvarchar(256)
);
create table OtherTable1
(
ID int IDENTITY primary key,
MainTableID int foreign key references MainTable(ID)
);
create table OtherTable2
(
ID int IDENTITY primary key,
MainTableID int foreign key references MainTable(ID)
);
-- and so on
insert into MainTable (MyField) values('A');
insert into MainTable (MyField) values('BB');
insert into MainTable (MyField) values('CCC');
insert into MainTable (MyField) values('DDDD');
insert into MainTable (MyField) values('FFFFF');
insert into OtherTable1 (MainTableID) values(1);
insert into OtherTable1 (MainTableID) values(2);
insert into OtherTable2 (MainTableID) values(3);
Result i need:
MainTable
ID MyField
4 DDDD
5 FFFFF
Query should return
A
BB
CCC

Answer 1

You need dynamic SQL for this.
You can use the system views to pull out the foreign key information and build up a dynamic statement, either SELECT or DELETE.
DECLARE #sql nvarchar(max) = '
SELECT t.MyField
-- alternately DELETE t
FROM MainTable t
WHERE ' + (
SELECT STRING_AGG(CAST(
'
NOT EXISTS (SELECT 1
FROM ' + QUOTENAME(s.name) + '.' + QUOTENAME(t.name) + ' t2.
WHERE ' + c.ForeignKeys + ')
'
AS nvarchar(max)), '
AND '
)
FROM sys.tables MyTable
JOIN sys.foreign_keys fk ON fk.referenced_object_id = MyTable.object_id
JOIN sys.tables t ON t.object_id = fk.parent_object_id
JOIN sys.schemas s ON s.schema_id = t.schema_id
OUTER APPLY (
SELECT STRING_AGG('t2.' + QUOTENAME(c.name) + ' = t.' + QUOTENAME(cMyTable.name), ' AND ')
FROM sys.foreign_key_columns fkc
JOIN sys.columns c ON c.object_id = fk.parent_object_id AND c.column_id = fkc.parent_column_id
JOIN sys.columns cMyTable ON cMyTable.object_id = MyTable.object_id AND cMyTable.column_id = fkc.referenced_column_id
WHERE fkc.constraint_object_id = fk.object_id
) c(ForeignKeys)
WHERE MyTable.name = 'MainTable'
);
PRINT #sql; -- for testing
EXEC sp_executesql #sql;
db<>fiddle