What is a correlated sub-query? How can these queries be useful?

Questions to ask a SQL Server database developer applicant

(Continued from previous question...)

What is a correlated sub-query? How can these queries be useful?

The more seasoned developer will be able to accurately describe this type of query.
A correlated sub-query is a special type of query containing a sub-query. The sub-query contained in the query actually requests values from the outside query, creating a situation similar to a loop. You can find a more detailed description as to how these special types of queries work in this article.

Other Interview Questions

• Can you give me an overview of some of the database objects available for use in SQL Server 2000?
• What is an index? What types of indexes are available in SQL Server 2000?
• What does NULL mean?
• What is a primary key? What is a foreign key?
• What are triggers? What are the different types of triggers in SQL Server 2000?
• How can you ensure that a table named TableB with a field named Fld1 will only have those values in the Fld1 field that are also in the table named TableA with a field named Fld1?
• What is a performance consideration of having too many indexes on a production online transaction processing (OLTP) table?
• What can be used to ensure that a field in a table only accepts a certain range of values?
• What is the difference between a return parameter and an OUTPUT parameter?
• What is a correlated sub-query? How can these queries be useful?