SQL Merge n rows from source table to two targets - sql

Question

We have an old database that we maintain, and a new one that we have started using. We need to periodically transfer data from the old db to the new one. At the moment, we need to transfer, or merge as it might also be called, data from one table - Student, in the old database to two tables (ie two targets) in the new one - Person and Student. Now the catch is that the data from the old, source, database should be divided among the two tables in the new one. For example (just for the sake of this post),
Old table 'Student'
------------------------------
IdNo | FirstName | LastName |
578 | John | Doe |
645 | Sara | Doe |
New table 'Person'
-----------
Id | IdNo |
11 | 578 |
23 | 645 |
New table 'Student'
--------------------------------------
Id | PersonId | FirstName | LastName |
101| 11 | John | Doe |
102| 23 | Sara | Doe |
And the procedure should take a parameter of the number of rows to merge.
How can this be accomplished?
Update
Perhaps it would be easier for you guys to know what I mean by pseudo code:
MERGE [NewDB].[dbo].[Person] p, [NewDB].[dbo].[Student] ns -- 2 targets, this does not work
USING [OldDB].[dbo].[student] os -- source table, old student
ON p.IdNo = s.IdNo
WHEN MATCHED THEN -- Update existing rows
UPDATE p
SET p.SomeCoumn1 = os.SomeColumn1 -- works. os (old student) is know here
UPDATE ns
SET ns.SomeColumn2 = os.SomeColumn2 -- Does not work. os is not known here
WHEN NOT MATCHED BY TARGET THEN -- Add new rows
INSERT INTO p (IdNo, SomeOlumn1)
VALUES (os.Idno, os.SomeColumn1); -- os (old Studnet) is known here
INSERT INTO ns (SomeColumn2)
VALUES (os.SomeColumn2); -- Does not work. os is not knwon here
I hope that makes it somewhat clearer.

Answer 1

May we assume the reason you want to do this in one statement instead of two is that one if the fields in the first table you are inserting in to is an identity field (Id in the Person table in your example) that needs to be inserted into the second table?
If so, add an OUTPUT clause in the first merge statement so that you have the relationship and fields you require for the second merge statement.
declare #OldStudent table (IdNo int, FirstName varchar(30), LastName varchar(30))
declare #Person table (Id int identity, IdNo int)
declare #NewStudent table (Id int identity, PersonId int, FirstName varchar(30), LastName varchar(30))
insert #OldStudent (IdNo, FirstName, LastName)
select 578, 'John', 'Doe'
union all select 645, 'Sara', 'Doe'
declare #output table ([Action] varchar(20), PersonId int, IdNo int)
MERGE #Person p
USING #OldStudent os
ON p.IdNo = os.IdNo
WHEN MATCHED THEN -- Update existing rows
UPDATE SET IdNo = os.IdNo
WHEN NOT MATCHED BY TARGET THEN -- Add new rows
INSERT (IdNo) VALUES (os.Idno)
OUTPUT $action, inserted.Id, inserted.IdNo into #output;
WITH src AS
(
select
o.IdNo, o.PersonId, os.FirstName, os.LastName
from
#output o
inner join #OldStudent os on os.IdNo = o.IdNo
)
MERGE INTO #NewStudent as ns
USING src
ON src.PersonID = ns.PersonID
WHEN MATCHED THEN
UPDATE SET FirstName = src.FirstName, LastName = src.LastName
WHEN NOT MATCHED BY TARGET THEN -- Add new rows
INSERT (PersonID, FirstName, LastName) VALUES (src.PersonID, src.FirstName, src.LastName);
select * from #Person
select * from #NewStudent