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Question 21 :

What is a primary key? What is a foreign key?

Answer :

A primary key is the field(s) in a table that uniquely defines the row in the table; the values in the primary key are always unique. A foreign key is a constraint that establishes a relationship between two tables. This relationship typically involves the primary key field(s) from one table with an adjoining set of field(s) in another table (although it could be the same table). The adjoining field(s) is the foreign key.


Question 22 :

What are triggers? What are the different types of triggers in SQL Server 2000?

Answer :

It's very beneficial for a potential database developer to know the types of triggers available, and how to implement them.

A trigger is a specialized type of stored procedure that is bound to a table or view in SQL Server 2000. In SQL Server 2000, there are INSTEAD-OF triggers and AFTER triggers. INSTEAD-OF triggers are procedures that execute in place of a Data Manipulation Language (DML) statement on a table. For example, if I have an INSTEAD-OF-UPDATE trigger on TableA, and I execute an update statement on that table, the code in the INSTEAD-OF-UPDATE trigger will execute instead of the update statement that I executed.

An AFTER trigger executes after a DML statement has taken place in the database. These types of triggers are very handy for auditing data changes that have occurred in your database tables.


Question 23 :

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?

Answer :

This relationship related question has two potential answers. The first answer (and the one that you want to hear) is the use of foreign key constraints. A foreign key constraint is used to maintain referential integrity. It is used to ensure that a field in a table will only hold values that are already defined in another field in a different (or the same) table. That field is the candidate key (usually a primary key of the other table).

The other option is the use of triggers. Triggers can be used to ensure the same effect of constraints in a roundabout way, but it is much more difficult to set up and maintain, and the performance is typically worse. Because of this, Microsoft recommends that developers use foreign key constraints instead of triggers for maintaining referential integrity.


Question 24 :

What is a performance consideration of having too many indexes on a production online transaction processing (OLTP) table?

Answer :

You are looking for the applicant to make some reference regarding data manipulations. The more indexes on a table, the more time it takes for the database engine to update, insert, or delete data, as the indexes all have to be maintained as the data manipulation occurs.


Question 25 :

What can be used to ensure that a field in a table only accepts a certain range of values?

Answer :

This question can be answered a couple of different ways, but only one answer is a "good" one. The answer you want to hear is a Check constraint, which is defined on a database table that limits the values entered into that column. These constraints are relatively easy to create, and they are the recommended type for enforcing domain integrity in SQL Server.

Triggers can also be used to restrict the values accepted in a field in a database table, but this solution requires the trigger to be defined on the table, which can hinder performance in certain situations. For this reason, Microsoft recommends Check constraints over all other methods for restricting domain integrity.