Question

I the following two tables/columns:

TableA
id | data

TableB
fkeyA1 | fkeyA2 | fkeyA3 | name

The first three columns in TableB are foreign keys all pointing to TableA. I would like to transform TableB into the following two tables:

TableC
id | name

TableD
fkeyC | fkeyA

so that one row in TableB becomes one row in TableC plus three rows in TableD. How should I write a SQL query for this?

EDIT:

In TableB, there is a unique index on (fkeyA1, fkeyA2, fkeyA3), but the name column does not necessarily have unique values.

Answer 1

You can use a cursor statement:

declare @idC table(id int)
declare @fkeyC int, @fkeyA1 int, @fkeyA2 int, @fkeyA3 int, @name varchar(8)
declare CursorB cursor fast_forward for select fkeyA1, fkeyA2, fkeyA3, name from TableB
open CursorB
fetch next from CursorB into @fkeyA1, @fkeyA2, @fkeyA3, @name
while @@fetch_status = 0
begin
    insert into TableC(name) output inserted.id into @idC values (@name)
    set @fkeyC = (select top 1 id from @idC)
    insert into TableD(fkeyC, fkeyA) values (@fkeyC, @fkeyA1), (@fkeyC, @fkeyA2), (@fkeyC, @fkeyA3)
    delete from @idC
    fetch next from CursorB into @fkeyA1, @fkeyA2, @fkeyA3, @name
end
close CursorB
deallocate CursorB

This may not be the best in performance, but will allow for non-unique values for the name column.