I'm not sure if I've completely fudged the design of my small hobby database (I'm not a DBA by any means), but I have a table like this (primary key is
staffid | target | effectivefrom --------|--------|--------------- 1 | 6.0 | 2012-01-01 2 | 6.0 | 2012-01-01 3 | 6.0 | 2012-01-01 1 | 7.0 | 2012-03-01
So basically, three staff all start out with a target of 6.0, but on March, staff with ID 1 has a new target of 7.0. I want to maintain historical targets because it is relevant to other data in other tables.
I would like to have a user-defined function that takes a date as a parameter, and this function needs to join the above table with another table based on the date. Say the function is called with 1st of February as the date, I would like the result of the join to include the target column showing 6.0 for all staff.
Something like this (I think this won't work because there could be multiple rows before
SELECT othertable.*, targets.target FROM othertable JOIN targets ON othertable.staffid = targets.staffid AND targets.effectivedate <= dateParameter;
Please let me know if I have done an absolute DBA 'no-no' or whether I just need some caffeine.