WHERE Clause sorting via String

Question

Hi, I am joining 2 tables together while using DISTINCT in the Select statement but i need to sort all the rows that only match by Date '1996'. Problem is the conversion of the Date/Time value is not a String i need to return only the rows where companies
only placed orders in 1996.
I have also tried WHERE o.OrderDate LIKE '[1996]%'
Select DISTINCT CompanyName
From Customers c
JOIN Orders o ON o.OrderDate = c.CompanyName
WHERE o.OrderDate = '1996'
Order By CompanyName ASC;

Answer 1

I have to use DISTINCT & JOIN both tables it is apart of my assignment i have no choice in the matter.
I don't care what your professor tells you. I care that you learn SQL properly. And, hey, chances are good that I know T-SQL better than your professor.
DISTINCT is a highly abused keyword. To the extent that I would say that anytime you feel compelled to put in DISTINCT, you should start thinking if you might have gone wrong somewhere in the query. In a properly written join, there is rarely a need for
DISTINCT. If it happens, it may be one of the following:
1) Incomplete join-conditions. You joined two tables on a single column, when there is a two-column key linking them. That is, an error in the query.
2) The table that introduces duplicates in the query is not included in the SELECT list, because the table only appears in the query to check existence. This is your case, and you should use EXISTS instead (no matter what your professor asks you for).
3) You only include a subset of the columns from the tables in the query, and in those columns alone there is a duplicate. This may be a legit case, because you may only be looking for the distinct values. But you should review the requirements first.
I don't list these points because I am bored on a Saturday night. I list these points, because I see these errors over and over again by inexperienced programmers on the forums. And for that matter not-so-inexperienced programmers who once learnt bad
habits, and still are sticking to them.
So, OK, show your professor the query with JOIN and DISTINCT. But also show him the query with EXISTS. Also make sure that you understand how that query works. Your professor may or may not be impressed, but that does not matter. You learn for life, and
not to impress your professor.
And, oh, one more thing. The condition on OrderDate should really be:
 AND  O.OrderDate >= '19960101'
 AND  O.OrderDate < '19970101'
This is guaranteed to do an IndexSeek on OrderDate if the optimizer finds that this is the best solution. (Which it will not in this case, because you are looking at one third of all orders.) On the other hand, the condition that Ronen is trying to lure
you to use:
   WHERE datepart(year,o.OrderDate) = 1996
may or may not seek the index, depending on how the optimizer is implemented this year.
I realise that the talk about indexes and optimizer may go above your head at this point, but again, I am eager that you learn best practices early, and that you don't learn things you will need to unlearn later. You can remember this lesson in this
way: never entangle a column into an expression, if you can resolve the condition with simple comparison operations.
Erland Sommarskog, SQL Server MVP, [email protected]