Question

I have a database where I need to query to get records from one table and then lookup on another table to see if that value exists there. That table might return multiple records and I want the one with the most recent date.

So table 1 is basically:

ID (Primary Key) Name Test_Score 

And Table 2 is

Test_Id (Primary) Student_ID (Foreign Key) Test_Score Test_Date 

As I’m going through the records, if the no tests exist in table 2 for the Student_id, I want to use the score in table 1, otherwise I want to use the score from table 2 with the most recent date. I have this all working in C# code, but the clients want it in a stored procedure for reporting purposes and I’m seeing some performance issues since the tables are quite large. Also, this basic example actually happens multiple times against multiple tables.

I’m sure there is an elegant way of doing this that is fast and efficient, but I can’t seem to come up with anything but using a cursor.

Does someone know the straight forward solution?

Answer 1

Not 100% percent sure about syntactical details, but something like this:

select table1.Name, ISNULL(table2.Test_Score, table1.Test_Score) from    table1   left outer join table2     on table1.id = table2.Student_ID     AND table2.Test_Date = (       select max(x.Test_Date)       from table2 x       where table1.id = x.Student_ID       group by x.Student_ID) 

If the subquery is not allowed where it is, move it to the where clause. (Sorry, i can’t try it where i am now.)

The query only works if the Test_Date is unique. If not, you get repeated results. Then you should use a Group By

select table1.Name, min(ISNULL(table2.Test_Score, table1.Test_Score)) from    table1   left outer join table2     on table1.id = table2.Student_ID     AND table2.Test_Date = (       select max(x.Test_Date)       from table2 x       where table1.id = x.Student_ID       group by x.Student_ID) group by table1.id, table1.Name