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.
Upcoming Questions
What are triggers? What are the different types of triggers in SQL Server 2000?
Posted by Devin 3 days ago (Editorial)
What is a primary key? What is a foreign key?
Posted by Devin 3 days ago (Editorial)
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.
What does NULL mean?
Posted by Devin 3 days ago (Editorial)
The value NULL is a very tricky subject in the database world, so don't be surprised if several applicants trip up on this question.
The value NULL means UNKNOWN; it does not mean '' (empty string). Assuming ANSI_NULLS are on in your SQL Server database, which they are by default, any comparison to the value NULL will yield the value NULL. You cannot compare any value with an UNKNOWN value and logically expect to get an answer. You must use the IS NULL operator instead.
The value NULL means UNKNOWN; it does not mean '' (empty string). Assuming ANSI_NULLS are on in your SQL Server database, which they are by default, any comparison to the value NULL will yield the value NULL. You cannot compare any value with an UNKNOWN value and logically expect to get an answer. You must use the IS NULL operator instead.
What is an index? What types of indexes are available in SQL Server 2000?
Posted by Devin 3 days ago (Editorial)
Any experienced database developer should be able to answer this question with ease. Some of the less-experienced developers will be able to answer it, but with a little less clarity.
In its most simple terms, an index is a data structure used to provide quick access to data in a database table or view. In SQL Server, they come in two flavors: clustered and non-clustered. Clustered indexes store the data at the leaf level of the index. This means that whichever field(s) in your table are included in the clustered index, they will be stored in an orderly fashion in the table. Because of this sorting, you can only have one clustered index per table. Non-clustered indexes contain a row identifier at the leaf level of the index. This row identifier is a pointer to a location of the data on the disk. This allows you to have more than one non-clustered index per table.
In its most simple terms, an index is a data structure used to provide quick access to data in a database table or view. In SQL Server, they come in two flavors: clustered and non-clustered. Clustered indexes store the data at the leaf level of the index. This means that whichever field(s) in your table are included in the clustered index, they will be stored in an orderly fashion in the table. Because of this sorting, you can only have one clustered index per table. Non-clustered indexes contain a row identifier at the leaf level of the index. This row identifier is a pointer to a location of the data on the disk. This allows you to have more than one non-clustered index per table.
Can you give me an overview of some of the database objects available for use in SQL Server 2000?
Posted by Devin 3 days ago (Editorial)
You are looking for objects such as: tables, views, user-defined functions, and stored procedures; it's even better if they mention additional objects such as triggers. It's not a good sign if an applicant cannot answer this basic question.
What is Isolation Level?
Posted by Devin 3 days ago (Editorial)
An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. A lower isolation level increases concurrency, but at the expense of data correctness. Conversely, a higher isolation level ensures that data is correct, but can affect concurrency negatively. The isolation level required by an application determines the locking behavior SQL Server uses. SQL-92 defines the following isolation levels, all of which are supported by SQL Server:
Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read).
Read committed (SQL Server default level).
Repeatable read.
Serializable (the highest level, where transactions are completely isolated from one another).
Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read).
Read committed (SQL Server default level).
Repeatable read.
Serializable (the highest level, where transactions are completely isolated from one another).
What is Transaction?
Posted by Devin 3 days ago (Editorial)
A transaction is a sequence of operations performed as a single logical unit of work. A logical unit of work must exhibit four properties, called the ACID (Atomicity, Consistency, Isolation, and Durability) properties, to qualify as a transaction.
What are the constraints ?
Posted by Devin 3 days ago (Editorial)
Table Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity. SQL Server 2000 supports five classes of constraints. NOT NULL , CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY.
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