SQL Interview Questions

[sony]

Guys, let's share some important SQL Interview Questions.

[imtiaz]

"Where" is a kind of restriction statement. You use where clause to restrict all the data from DB. Where clause is using before result retrieving. But Having clause is using after retrieving the data. Having clause is a kind of filtering command.

[imtiaz]

What is "normalization"? Why do you sometimes want to denormalize?

Normalizing data means eliminating redundant information from a table and organizing the data so that future changes to the table are easier. Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data processing.