Question

I’m having trouble understanding the different join algorithms (nested-loop join, merge join, index join, hash join, and other variations) and how/when to use them. More specifically, I’ve been asked to draw a query tree for the most efficient execution of the following query:

SELECT E.Name
FROM Employee E, Department D, Works_On W, Project P
WHERE E.DNO = D.DNO and E.SSN = W.ESSN and P.PNUM = W.PNUM and
    P.Budget > 50 and E.Sex = 'M' and E.Hobby = 'Yodeling' and
    D.DName = 'Rational Mechanics';

I can provide the schema if it’s needed; basically, the four tables are

Employee (SSN, Name, DNO – Department number, Salary, Sex),
Department (DNO, DName, Budget, Location, MGRSSN),
Works_On (ESSN, PNum – Project number),
Project (PNum, PName, Budget, Location, Goal).

I’ve drawn a left deep join tree and I don’t know which algorithm to use for each join.
If I could get an explanation of when to use each algorithm or a pointer to a resource that explains it, that would be very helpful.

Edit: I’m not asking about how to specify different joins in sql, only about the joins in general. Also, I was not told that any of the tables were indexed, but I was told that I can index just to do an index join. I was also given statistics to make the query tree heuristically, which I used to make the structure of the tree.

Answer 1

msdn is a good resource for this info. technet.microsoft.com/en-us/library/ms191426(v=sql.105).aspx

is exactly what I needed. Thanks, Zeph!