Monday, July 20, 2009

Difference between a "where" clause and a "having" clause.?

Having clause is used only with group functions whereas Where is not used with.

Q: What's the difference between a primary key and a unique key?

A: Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

Unique Key : unique values
Primary Key : Not Null + Unique + nonclustered index


  1. Good day! just passing by your site to read some interesting facts. Thank you for sharing your article, I must say that you did a good job and continue to inspire us. Try to visit my site

  2. I read your blog.I thought it was great.. Hope you have a great day. God bless.


  3. I was also checking one of the query and came to your blog. I must say, this is the place one should visit before going to interview.

    Thanks buddy. Please create same blog for selenium also. Good Luck.