SQL Server 2008 - Table - Clarifications

Question

I am new to SQL Server 2008 database development.

Here I have a master table named 'Student' and a child table named 'Address'. The common column between these tables is 'Student ID'.

My doubts are:

1. Do we need to put 'Address Id' in the 'Address' table and make it primary key? Is it mandatory? ( I won't be using this 'Address Id' in any of my reports )

2. Is Primary key column a must in any table?

Would you please help me on these.

Would you please also refer best links/tutorials for SQL Server 2008 database design practices (If you are aware of) which includes naming conventions, best practices, SQL optimizations etc. etc.

Answer 1

1) Yes, having an ADDRESS_ID column as the primary key of the ADDRESS table is a good idea.

But having the STUDENT_ID as a foreign key in the ADDRESS table is not a good idea. This means that an address record can only be associated to one student. Students can have roommates, so they'd have identical addresses. Which comes back to why it's a good idea to have the ADDRESS_ID column as a primary key, as it will indicate a unique address record.

Rather than have the STUDENT_ID column in the ADDRESS table, I'd have a corrollary/xref/lookup table between the STUDENT and ADDRESS tables:

STUDENT_ADDRESSES_XREF

• STUDENT_ID , pk, fk to STUDENTS table
• ADDRESS_ID , pk, fk to ADDRESS table
• EFFECTIVE_DATE , date, not null
• EXPIRY_DATE , date, not null

This uses a composite primary key, so that only one combination of the student & address exist. I added the dates in case there was a need to know when exactly, because someone could move back home/etc after all.

Most importantly, this works off the ADDRESS_ID column to allow for a single address to be associated to multiple people.

2) Yes, defining a primary key is frankly a must for any table.

In most databases, the act also creates an index - making searching more efficient. That's on top of the usual things like making sure a record is a unique entry...

Answer 2

Every table should have a way to uniquely and unambiguously identify a record. Make AddressID the primary key for the address table.

Without a primary key, the database will allow duplicate records; possibly creating join problems or trigger problems (if you implement them) down the road.