Question

I am trying to copy data from an old database into a new one, and transform it to follow the new db structure. The old one looked something like this:

Table 1:

Id | Col A 
----------
1      0
2      8
3      7
4      1

In the new database, Table 1 now looks like this, where the data from col A is now in another table, and it’s linked back to Table 1 via the A_Id foreign key column:

Table 1:

Id | A_Id_FK
----------
1      0
2      1
3      2
4      3

Table 2:

Id | Col A
----------
0      0
1      8
2      7
3      1

So…I’m very rusty with my SQL skills. I need a one time (read: speed doesn’t matter) query to create the Table 2 records while simultaneously linking them to the Table 1 records. Another point to mention is that I have two databases. One is the old one with Table 1, and the other is the new one with an empty Table 2, and a Table 1 that has all the other info aside from the A_Id_FK, which for now is just linked to an empty record in Table 2 for each record.

Thanks in advance.

Edit – For some extra clarity, Table 2 in the new DB is empty. Col A in the old database is NOT a unique number (in fact, it’s not a number at all, but it’s just that way for simplicity). Table 1 in the new database is populated, but the value in A_Id_FK is set to 1 for everything just to have a valid foreign key. Lastly, even identical Col A records need their own instance in the new db.

Answer 1

You can use CURSOR (Table_2.id is identity):

DECLARE @id INT
DECLARE @col_a VARCHAR(50)
DECLARE db_cursor CURSOR FOR 
    SELECT id, col_a
    FROM Table_Source

OPEN db_cursor  
    FETCH NEXT FROM db_cursor INTO @id, @col_a

WHILE @@FETCH_STATUS = 0  
BEGIN  
    INSERT INTO Table_2 (col_a) VALUES (@col_a)
    INSERT INTO Table_1 (id, fk) VALUES (@id, @@IDENTITY)

    FETCH NEXT FROM db_cursor INTO @id, @col_a
END  

CLOSE db_cursor  
DEALLOCATE db_cursor