SQL Server stored procedure - reference two tables

Question

I am trying to create a select stored procedure where it takes a value from one table and sets this as a parameter for the second table.

As below I would like the user to input a reference number, which then gathers the registration ID from table 1, then performs a search in table two based on the registration ID, reference number and registration ID are both unique.

Reference number only exists in tableOne, registration_id exists in both

CREATE PROCEDURE SPSelect1
    @Reference_Number NVARCHAR(10),
    @Registration_ID NVARCHAR(10)
AS
    SET @Registration_ID = (tblOne.registration_id WHERE reference_number = @Reference_Number)

    SELECT * 
    FROM tblTwo 
    WHERE tblTwo.registration_id = @Registration_ID
END

Answer 1

The correct syntax is this:

SET @Registration_ID = (SELECT tblOne.registration_id where reference_number = @Reference_Number)

Or you could combine the two statements using a JOIN:

SELECT tblTwo.*
FROM   tblTwo
JOIN   tblOne ON tblTwo.registration_id = tblOne.registration_id
WHERE  tblOne.reference_number = @Reference_Number

Answer 2

You could use:

select * 
from tblTwo 
where tblTwo.registration_id IN (SELECT tblOne.registration_id
                                 FROM tblOne
                                 WHERE reference_number = @Reference_Number)

Answer 3

i would like the user to input a reference number

Then your stored proc should only require a reference number as an input parameter. It can then query tblOne to find the registration ID corresponding to that reference number, and then query tblTwo using the registration ID in it's WHERE clause.

reference number and registration ID are both unique

Since you specified that the two fields are unique, I would use an INNER JOIN :

CREATE PROCEDURE SPSelect1
    @Reference_Number NVARCHAR(10)

AS

BEGIN 
    SELECT *
    FROM tblTwo
    INNER JOIN tblOne
    ON tblTwo.Registration_ID = tblOne.Registration_ID
    WHERE tblOne.Reference_Number = @Reference_Number                                        
END

GO