How to add rows to second table from the first table using Common table expression in SQL Server - sql

Question

For example, I have the first table and I want to fill the second table using the first table.
Table A
Name A B C D
-----------------------
name1 a1 b1 c1 d1
name2 a2 b2 c2 d2
Table B (Desired Format)
ID Name Code
----------------------
1 name1 a1
2 name1 b1
3 name1 c1
4 name1 d1
5 name2 a2
6 name2 b2
7 name2 c2
8 name2 d2
As per the suggestions of #Surendra Nath GM, I tried this
DECLARE #counter as int
SET #counter = 1;
;WITH Actual AS
(
SELECT ROW_NUMBER() OVER( ORDER BY IDKEY) as ID FROM Northwind.dbo.Table1
WHERE
),FIRST AS
(
SELECT ((ROW_NUMBER() OVER( ORDER BY IDKEY))*4-3) AS ID,Name, A
FROM Northwind.dbo.Table1
),SECOND AS
(
SELECT ((ROW_NUMBER() OVER( ORDER BY IDKEY))*4-2) AS ID, Name ,B
from Northwind.dbo.Table1
), NEXT AS
(
SELECT ((ROW_NUMBER() OVER( ORDER BY IDKEY))*4-1) AS ID, Name, C
from Northwind.dbo.Table1next
), ________ as
(
SELECT ((ROW_NUMBER() OVER( ORDER BY IDKEY))*4) AS ID, Name, D
from Northwind.dbo.Table1
)
#counter = #counter+1;
)
SELECT * FROM FIRST
UNION ALL
SELECT * FROM SECOND
UNION ALL
SELECT * FROM NEXT
UNION ALL
SELECT * FROM _________
ORDER BY ID
Here, what do I use after the "SECOND AS". I tried writing "THIRD AS" but apparently no such command exists so after some searching, I could write the third row using "NEXT AS" but I am completely clueless as to how do I insert the Fourth row.
I know I can simply write 4 insert commands for each of A,B,C and D but then I will get the not codes in the following order which is NOT desired:
Table B(NOT DESIRED IN THIS FORMAT)
ID Name Code
----------------------
1 name1 a1
2 name2 a2
3 name1 b1
4 name2 b2
5 name1 c1
6 name2 c2
7 name1 d1
8 name2 d2
Also, the desired format can be achieved using simple loops but in the project I am working on, there are around 200000 rows and the simple loops method takes a lot of time. So, I want to do it using CTE. Please help.

Answer 1

You can do it with two inserts:
insert into tableB(A, B)
select A1, B1
from tableA;
insert into tableB(A, B)
select A2, B2
from tableA;
Or union the table with one insert:
insert into tableB(A, B)
select A1, B1
from tableA union all
select A2, B2
from tableA;
This assumes that id is defined as id int indentity(1, 1) so it automatically increments.
If not, you could assign it as:
insert into tableB(id, A, B)
select row_number() over (order by (select NULL)) as id, A1, B1
from (select A1, B1
from tableA union all
select A2, B2
from tableA
) t

Answer 2

getting the ID will be the tricky part over here, in order to do that and use the set opertaions, you have to split the job into two and generate odd ID's for the select of A1,B1 and generate event ID's for the select of A2,B2
Shown as below
;WITH Actual AS
(
SELECT ROW_NUMBER() OVER( ORDER BY Name) as RN, * FROM Table1
),FIRST AS
(
SELECT ((RN*2)-1) AS ID,A1,B1
FROM TABLE1
ORDER BY RN
),SECOND AS
(
SELECT (RN*2) AS ID,A2,B2
FROM TABLE1
ORDER BY RN
)
SELECT * FROM FIRST
UNION ALL
SELECT * FROM SECOND
if you have four columns then you can use the below query instead
;WITH Actual AS
(
SELECT ROW_NUMBER() OVER( ORDER BY Name) as RN, * FROM Table1
),FIRST AS
(
SELECT ((RN*2)-1) AS ID,A1,B1,C1,D1
FROM TABLE1
ORDER BY RN
),SECOND AS
(
SELECT (RN*2) AS ID,A2,B2,C2,D2
FROM TABLE1
ORDER BY RN
)
SELECT * FROM FIRST
UNION ALL
SELECT * FROM SECOND