What is Trigger?

A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.

Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.

What are the different index configurations a table can have?

A table can have one of the following index configurations:

No indexes
...

A clustered index
A clustered index and many nonclustered indexes
A nonclustered index
Many nonclustered indexes

Differences between star and snowflake schema?

Star schema –

A single fact table with N number of Dimension, all dimensions will be linked directly with a fact table. This schema is de-normalized and results in simple join and less complex query as well as faster results.
...

Snow schema –

Any dimensions with extended dimensions are know as snowflake schema, dimensions maybe interlinked or may have one to many relationship with other tables. This schema is normalized and results in complex join and very complex query as well as slower results.

Can SQL Servers linked to other servers like Oracle?

SQL Server can be lined to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has a OLE-DB provider for oracle that Microsoft provides to add it as linked server to the SQL Server group.

What is VLDB?

VLDB is an abbreviation of Very Large DataBase. A one terabyte database would normally be considered to be a VLDB. Typically, these are decision support systems or transaction processing applications serving large numbers of users.

What is LINQ?

Language Integrated Query (LINQ) adds the ability to query objects using .NET languages. The LINQ to SQL object/relational mapping (O/RM) framework provides the following basic features:
Tools to create classes (usually called entities) mapped to database tables

...Compatibility with LINQ’s standard query operations
The DataContext class, with features such as entity record monitoring, automatic SQL statement generation, record concurrency detection, and much more

What is the use of EXCEPT Clause?

EXCEPT clause is similar to MINUS operation in Oracle. The EXCEPT query and MINUS query returns all rows in the first query that are not returned in the second query. Each SQL statement within the EXCEPT query and MINUS query must have the same number of fields in the result sets with similar data types.