Sql Server Interview Questions Ans Part-3

Q#26. Can we rename a column in the output of SQL query?

Ans. Yes by using the following syntax we can do this.

SELECT column_name AS new_name FROM table_name;

Q#27. What is the difference between a Local and a Global temporary table?

Ans. If defined in inside a compound statement a local temporary table exists only for the duration of that statement but a global temporary table exists permanently in the database but its rows disappear when the connection is closed.

Q#28. What is the SQL Profiler?

Ans. SQL Profiler provides a graphical representation of events in an instance of SQL Server for the monitoring and investment purpose. We can capture and save the data for further analysis. We can put filters as well to captures the specific data we want.

Q#29. What do you mean by authentication modes in SQL Server?

Ans. There are two authentication modes in SQL Server.

• Windows mode
• Mixed Mode – SQL and Windows.

Q#30. How can we check the SQL Server version?

Ans. By running the following command:

SELECT @@Version

Q#31. Is it possible to call a stored procedure within a stored procedure?

Ans. Yes, we call a stored procedure within a stored procedure It is called recursion property of SQL server and these type of stored procedures are called nested stored procedures.

Q#32. What is SQL Server Agent?

Ans. SQL Server agent allows us to schedule the jobs and scripts. It helps is implementing the day to day DBA tasks by automatically executing them on a scheduled basis.

Q#33. What is the PRIMARY KEY?

Ans. The primary key is a column whose values uniquely identify every row in a table. Primary key values can never be reused.

Q#34. What is a UNIQUE KEY constraint?

Ans. A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

Q#35. What is FOREIGN KEY

Ans. When a one table’s primary key field is added to related tables in order to create the common field which relates the two tables, it called a foreign key in other tables.

Foreign Key constraints enforce referential integrity.

Q#36. What is a CHECK Constraint?

Ans. A CHECK constraint is used to limit the values or type of data that can be stored in a column. They are used to enforce domain integrity.

Q#37. What are a Scheduled Jobs?

Ans. The scheduled job allows a user to run the scripts or SQL commands automatically on the scheduled basis. The user can determine the order in which commands need to execute and the best time to run the job to avoid the load on the system.

Q#38. What is a heap?

Ans. A heap is a table that does not contain any clustered index or non-clustered index.

Q#39. What is BCP?

Ans. BCP or Bulk Copy is a tool by which we can copy a large amount of data to tables and views. BCP does not copy the structures same as source to destination. BULK INSERT command helps to import a data file into a database table or view in a user-specified format.

Q#40. What is Normalization?

Ans. The process of table design to minimize the data redundancy is called normalization. We need to divide a database into two or more table and define relationships between them. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables.

Q#41. List the different normalization forms?

Ans. Different normalization forms are:

1NF (Eliminate Repeating Groups): Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.

2NF (Eliminate Redundant Data): If an attribute depends on only part of a multi-valued key, remove it to a separate table.

3NF (Eliminate Columns Not Dependent On Key): If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key.

BCNF (Boyce-Codd Normal Form): If there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.

4NF (Isolate Independent Multiple Relationships): No table may contain two or more 1:n or n:m relationships that are not directly related.

5NF (Isolate Semantically Related Multiple Relationships): There may be practical constraints on information that justifies separating logically related many-to-many relationships.

ONF (Optimal Normal Form): A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.

DKNF (Domain-Key Normal Form): A model free from all modification is said to be in DKNF.

Q#42. What is De-normalization?

Ans. De-normalization is the process of adding redundant data to a database to enhance the performance of it. It is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

Q#43. What is a Trigger and types of a trigger?

Ans. The trigger allows us to execute a batch of SQL code when a table event occurs (Insert, update or delete command executed against a specific table). Triggers are stored in and managed by DBMS. It can also execute a stored procedure.

2 types of triggers that are available in the SQL Server are as follows:

• DML Triggers: DML or Data Manipulation Language triggers are invoked whenever any of the DML commands like INSERT, DELETE or UPDATE happens on the table or on the view.
• DDL Triggers: DDL or Data Definition Language triggers are invoked whenever any changes occur in the definition of any of the database objects instead of actual data. These are very helpful to control the production and development of database environments.
• Logon Triggers: These are very special triggers which fire in case of the logon event of the SQL Server. This is fired before setup of a user session in the SQL Server.

Q#44. What is the Subquery?

Ans. A Subquery is a subset of select statements whose return values are used in filtering conditions of the main query. It can occur in a SELECT clause, FROM clause and WHERE clause. It nested inside a SELECT, INSERT, UPDATE, or DELETE statement or inside another subquery.

Types of Sub-query:

• Single-row sub-query: where the sub-query returns only one row
• Multiple-row sub-query: where the subquery returns multiple rows, and
• Multiple column sub-query: where the sub-query returns multiple columns

Q#45. What is a Linked Server?

Ans. Linked Servers is a concept by which we can connect another SQL server to a Group and query both the SQL Servers database using T-SQL Statements

sp_addlinkedsrvloginisssed to add link server.

Q#46. What is Collation?

Ans. Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case sensitivity, accent marks, kana character types and character width.

Q#47. What is View?

Ans. A view is a virtual table which contains data from one or more tables. Views restrict data access of the table by selecting only required values and make complex queries easy.

Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does data in the view, as views are the way to look at part of the original table. The results of using a view are not permanently stored in the database

Q#48. Where SQL server usernames and passwords are stored in a SQL server?

Ans. They get stored in System Catalog Views sys.server_principals and sys.sql_logins.

Q#49. What are the properties of a transaction?

Ans. Generally, these properties are referred to as ACID properties. They are:

• Atomicity
• Consistency
• Isolation
• Durability

Q#50. Define UNION, UNION ALL, MINUS, INTERSECT?

Ans. UNION – returns all distinct rows selected by either query.

UNION ALL – returns all rows selected by either query, including all duplicates.

MINUS – returns all distinct rows selected by the first query but not by the second.

INTERSECT – returns all distinct rows selected by both queries.