sql server dba interview questions

SQL Server DBA Interview Questions and Answers

Q.What are the different types of backups?

Answer: The SQL server offers 4 types of backups to suit the need of the administrator.

Complete backup :The complete back up is just zipping the content of the entire database in terms of the different tables and procedures etc. This back up can server as an independent entity that can be restored in different systems with just the base SQL server installed.

Transaction log backup: This is the mechanism of backing up the transaction logs that have been maintained in the server. This way the details of the database getting updated is obtained. This cannot be a stand-alone back up mechanism. But can save a lot of time if we already have the file system related to the DB backed up on the new deployment server.

Differential backup: This is a subset of the complete backup, where only the modified datasets are backed up. This can save the time when we are just trying to maintain a backup server to main server.

File backup: This is the quickest way to take the backup of entire database. Instead of taking in the data actually stored in DB, the files are backed up and the file system thus obtained when combined with the transaction logs of the original system will render the database that we are trying to back up.

Q.What are the different levels of isolation?

Answer: The isolation represents the way of separating the database from the effects of network accesses, thereby maintaining the consistency. The different levels of isolation are:

read committed: This level of isolation uses the shared locks and the reads to the database give the constant and consistent values.

read uncommitted: No locks implemented. This is the least effective isolation level. repeatable read: There are lock over the rows and values but the updates are maintained as a separate phantom row which is the next set of values for the specific record. Values can change within a specific transaction of a SQL function.

SERIALIZABLE reads: This is the implementation of pure lock mechanism where one specific transaction is not allowed access to specific record before another one completes.

Q.What are the steps to take to improve performance of a poor performing query?

Answer: Maximum use of indexes, stored procures should be done.

Avoid excessive use of complicated joins and cursors.

Avoid using conditional operators using columns of different tables.

Make use of computed columns and rewriting the query.

Q.What is normalization? Explain different levels of normalization?

Answer: Check out the article Q100139 from Microsoft knowledge base and of course, there’s much more information available in the net. It’ll be a good idea to get a hold of any RDBMS fundamentals text book, especially the one by C. J. Date. Most of the times, it will be okay if you can explain till third normal form.

Q.What is denormalization and when would you go for it?

Answer: As the name indicates, denormalization is the reverse process of normalization. It’s the controlled introduction of redundancy in to the database design. It helps improve the query performance as the number of joins could be reduced.

Q.How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

Answer: One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.

One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.

Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

It will be a good idea to read up a database designing fundamentals text book.

Q.What’s the difference between a primary key and a unique key?

Answer: Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.

Q.What are user defined datatypes and when you should go for them?

Answer: User defined datatypes let you extend the base SQL Server datatypes by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar(8). In this case you could create a user defined datatype called Flight_num_type of varchar(8) and use it across all your tables.

Q.What is bit datatype and what’s the information that can be stored inside a bit column?

Answer: Bit datatype is used to store boolean information like 1 or 0 (true or false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype can represent a third state, which is NULL.

Q.Define candidate key, alternate key, composite key.

Answer: A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys.

A key formed by combining at least two or more columns is called composite key.

Q.What are defaults? Is there a column to which a default can’t be bound?

Answer: A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can’t have defaults bound to them.

Q.What is a transaction and what are ACID properties?

Answer: A transaction is a logical unit of work in which, all the steps must be performed or none. ACID stands for Atomicity, Consistency, Isolation, Durability. These are the properties of a transaction. For more information and explanation of these properties, see SQL Server books online or any RDBMS fundamentals text book.

Q.Explain different isolation levels

Answer: An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. Here are the other isolation levels (in the ascending order of isolation): Read Uncommitted, Read Committed, Repeatable Read, Serializable. See SQL Server books online for an explanation of the isolation levels. Be sure to read about SET TRANSACTION ISOLATION LEVEL, which lets you customize the isolation level at the connection level.

Q.What type of Index will get created after executing the above statement?

Answer: Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise.

Q.What’s the maximum size of a row?

Answer: 8060 bytes. Don’t be surprised with questions like ‘what is the maximum number of columns per table’. Check out SQL Server books online for the page titled: “Maximum Capacity Specifications”.

Q.What is lock escalation?

Answer: Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it’s dynamically managed by SQL Server.

Q.What’s the difference between DELETE TABLE and TRUNCATE TABLE commands?

Answer: DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won’t log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back.

Q.Explain the storage models of OLAP

Answer: Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more infomation.

What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?

Q.What are constraints? Explain different types of constraints.

Answer: Constraints enable the RDBMS enforce the integrity of the database automatically, without needing you to create triggers, rule or defaults.

Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY

Q.Whar is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. what are the advantages and disadvantages of this approach?

Answer: Indexes are of two types. Clustered indexes and non-clustered indexes. When you craete a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and it’s row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table.

If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same t ime, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.

Database administration

Q.What is RAID and what are different types of RAID configurations?

Answer: RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance. MSDN has some information about RAID levels and for detailed information, check out the RAID advisory board’s homepage

Q.What are the steps you will take to improve performance of a poor performing query?

Answer: This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables.

Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.

Q.What are the steps you will take, if you are tasked with securing an SQL Server?

Answer: Again this is another open ended question. Here are some things you could talk about: Preferring NT authentication, using server, databse and application roles to control access to the data, securing the physical database files using NTFS permissions, using an unguessable SA password, restricting physical access to the SQL Server, renaming the Administrator account on the SQL Server computer, disabling the Guest account, enabling auditing, using multiprotocol encryption, setting up SSL, setting up firewalls, isolating SQL Server from the web server etc.

Q.What is a deadlock and what is a live lock? How will you go about resolving deadlocks?

Answer: Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other’s piece. Each process  would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user’s process.

A livelock is one, where a  request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.

Check out SET DEADLOCK_PRIORITY and “Minimizing Deadlocks”  in SQL Server books online. Also check out the article Q169960 from Microsoft knowledge base.

Q.What is blocking and how would you troubleshoot it?

Answer: Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first.

Q.Explain CREATE DATABASE syntax

Answer: Many of us are used to craeting databases from the Enterprise Manager or by just issuing the command: CREATE DATABAE MyDB. But what if you have to create a database with two filegroups, one on drive C and the other on drive D with log on drive E with an initial size of 600 MB and with a growth factor of 15%? That’s why being a DBA you should be familiar with the CREATE DATABASE syntax. Check out SQL Server books online for more information.

Q.How to restart SQL Server in single user mode? How to start SQL Server in minimal configuration mode?

Answer: SQL Server can be started from command line, using the SQLSERVR.EXE. This EXE has some very important parameters with which a DBA should be familiar with. -m is used for starting SQL Server in single user mode and -f is used to start the SQL Server in minimal confuguration mode. Check out SQL Server books online for more parameters and their explanations.

Q.As a part of your job, what are the DBCC commands that you commonly use for database maintenance?

Answer: DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc .

Q.What are statistics, under what circumstances they go out of date, how do you update them?

Answer: Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.

Some situations under which you should update statistics:

1) If there is significant change in the key values in the index

2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated

3) Database is upgraded from a previous version

Q.What are the different ways of moving data/databases between servers and databases in SQL Server?

Answer: There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP, logshipping, INSERT…SELECT, SELECT…INTO, creating INSERT scripts to generate data.

Q.What is database replicaion? What are the different types of replication you can set up in SQL Server?

Answer:  Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:

  • Snapshot replication
  • Transactional replication (with immediate updating subscribers, with queued updating subscribers)
  • Merge replication

See SQL Server books online for indepth coverage on replication. Be prepared to explain how different replication agents function, what are the main system tables used in replication etc.

How to determine the service pack currently installed on SQL Server?

The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. To know more about this process visit SQL Server service packs and versions.

Database programming (top)

Q.What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?

Answer:  Cursors allow row-by-row prcessing of the resultsets.

Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information.

Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip, where as a normal SELECT query makes only one rowundtrip, however large the resultset is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Furthere, there are restrictions on the SELECT statements that can be used with some types of cursors.

Most of the times, set based operations can be used instead of cursors. Here is an example:

If you have to give a flat hike to your employees using the following criteria:

Salary between 30000 and 40000 — 5000 hike

Salary between 40000 and 55000 — 7000 hike

Salary between 55000 and 65000 — 9000 hike

In this situation many developers tend to use a cursor, determine each employee’s salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below:

UPDATE tbl_emp SET salary =

CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000

WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000

WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000

END

Sql Server  DBA Interview Questions      Sql Server DBA Interview Questions and Answers

Q.Write down the general syntax for a SELECT statements covering all the options.

Answer: Here’s the basic syntax: (Also checkout SELECT in books online for advanced syntax).

SELECT select_list

[INTO new_table_]

FROM table_source

[WHERE search_condition]

[GROUP BY group_by_expression]

[HAVING search_condition]

[ORDER BY order_expression [ASC | DESC] ]

Q.What is a join and explain different types of joins.

Answer:  Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.

Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.

Q.What is the system function to get the current user’s user id?

Answer: USER_ID(). Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().

What are triggers? How many triggers you can have on a table? How to invoke a trigger on demand?

Answer: Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.

In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there’s no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder

Triggers can’t be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined.

Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.

Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers.

Also check out books online for ‘inserted table’, ‘deleted table’ and COLUMNS_UPDATED()

There is a trigger defined for INSERT operations on a table, in an OLTP system. The trigger is written to instantiate a COM object and pass the newly insterted rows to it for some custom processing. What do you think of this implementation? Can this be implemented better?

Instantiating COM objects is a time consuming process and since you are doing it from within a trigger, it slows down the data insertion process. Same is the case with sending emails from triggers. This scenario can be better implemented by logging all the necessary data into a separate table, and have a job which periodically checks this table and does the needful.

Q.What is a self join? Explain it with an example.

Answer: Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join.

CREATE TABLE emp

(

empid int,

mgrid int,

empname char(10)

)

INSERT emp SELECT 1,2,’Vyas’

INSERT emp SELECT 2,3,’Mohan’

INSERT emp SELECT 3,NULL,’Shobha’

INSERT emp SELECT 4,2,’Shridhar’

INSERT emp SELECT 5,2,’Sourabh’

SELECT t1.empname [Employee], t2.empname [Manager]

FROM emp t1, emp t2

WHERE t1.mgrid = t2.empid

Here’s an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses)

SELECT t1.empname [Employee], COALESCE(t2.empname, ‘No manager’) [Manager]

FROM emp t1

LEFT OUTER JOIN

emp t2

ON

t1.mgrid = t2.empid

Q.What is a deadlock and what is a live lock? How will you go about resolving deadlocks?

Answer:  A deadlock occurs when two or more processes waits for a resource that is acquired by or is under the control of another process. A live lock is similar to a deadlock except the process states keeps changing. The result of such state is that none of the process will be complete.

Deadlock detection finds and resolves deadlocks. A WFG strategy is followed. WFG is wait for graph. In WFG, processes are represented by nodes while dependencies are represented by edges. Thus, if process A is waiting for a resource held by process B, there is an edge in the WFG from the node for process A to the node for process B. a cycle is this graph is a deadlock. WFG constantly checks for cycles or when a process is blocked and adds a new edge to the WFG.   When a cycle is found, a victim is selected and aborted.

Q.What is blocking and how would you troubleshoot it?

Answer: Blocking occurs when two or more rows are locked by one SQL connection and a second connection to the SQL server requires a conflicting on lock on those rows. This results in the second connection to wait until the first lock is released.

Troubleshooting blocking:

SQL scripts can be written that constantly monitor the state of locking and blocking on SQL Server

The common blocking scenarios must be identified and resolved.

The scripts output must be checked constantly,

The SQL profilers data must be examined regularly to detect blocking.

Q.Explain the different types of BACKUPs available in SQL Server.

Answer: Complete database backup: This type of backup will backup all the information in the database. Used most commonly for disaster recovery and takes the longest time to backup.

Differential databse backup: The database is divided into partitions that have been modified since last complete backup. Most suitable for large databases. The most recent differential backup contains the changes from previous backups.

Transaction log backups: Backups only the changes logged in the transaction log. The transaction log has all changes logged about a database. Once the changes are accommodated on the database, the log is truncated or backed up.

File/File Group backups: used to recover individual files or file groups. Each filegroup can be individually backed up. This helps in recovery only the required file or filegroup for disaster recovery.

Q.What is database isolation in SQL Server?

Answer: Isolation in database defines how and when changes made by one transaction can be visible to other transactions. Different isolation levels are:

Serializable

Repeatable read

Read committed

Read uncommitted

Q.What is a Schema in SQL Server ? Explain how to create a new Schema in a Database?

Answer: A schema is used to create database objects. It can be created using CREATE SCHEMA statement. The objects created can be moved between schemas. Multiple database users can share a single default schema.

CREATE SCHEMA sample;

Table creation

Create table sample.sampleinfo

{

id int primary key,

name varchar(20)

}

Q.Explain how to create a Scrollable Cursor with the SCROLL Option.

Answer: Using the SCROLL keyword while declaring a cursor allows fetching of rows in any sequence

Example:

DECLARE employee_curs SCROLL CURSOR FOR SELECT * FROM employee;

The active set of the cursor is stored can be accessed in any order without the need of opening and closing the cursor. The Scroll cursors can be set for select and function cursors but not insert or update statements.

Q.Explain how to create a Dynamic Cursor with the DYNAMIC Option.

Answer:  When a cursor is declared as DYNAMIC, the cursor reflects all changes made to the base tables as the cursor is scrolled around.

Declare cursor_name cursor

[ STATIC | KEYSET | DYNAMIC | FAST_FORWARD ]

FOR select_statement

The dynamic option does not support ABSOLUTE FETCH.

Q.What are database files and filegroups?

Answer:  Database files are used for mapping the database over some operating system files. Data and log information are separate. SQL server database has three types of database files:

Primary: starting point of a database. It also points to other files in database. Extension: .mdf

Secondary: All data files except primary data file is a part of secondary files. Extension: .ndf

Log files: All log information used to recover database. Extension: .ldf

Q.Describe in brief Databases and SQL Server Databases Architecture.

Answer: SQL Server consists of a set of various components which fulfill data storage and data analysis needs for enterprise applications. Database architecture: All the data is stored in databases which is organized into logical components visible to the end users. It’s only the administrator who needs to actually deal with the physical storage aspect of the databases, whereas users only deal with database tables.

Every SQL Server instance has primarily 4 system database i.e. master, model, tempdb and msdb. All other databases are user created databases as per their needs and requirements.

A single SQL Server instance is capable of handling thousands of users working on multiple databases.

Q.How can you start the SQL Server in the single user mode and the minimal configuration mode?

Answer: The SQLServer.exe is the executable which can be called in the command prompt with the parameters -m and -f. These are the options that will start the SQL server in the user mode and minimal configuration mode respectively.

Q.How can you know that statistics should be updated?

Answer: Statistics represent the uniqueness for the indexes that are being used for selecting the records. This can make the query execution pretty efficient. The tables that we are dealing with if truncated and repopulated, there is a good chance that the indexes and statistics are out of sync and this is when we have to update the statistics. There are also other situations like when the table has been modified and lot of rows have been added recently or like when a server has been updated with different version of software. These also give us the reason to use the UPDATE_STATISTICS, DBCC SHOW_STATISTICS etc to update it accordingly.

Q.What is replication in SQL Server?

Answer: Replication refers to the moving or copying of the database elements from one system to another. This can be done in the SQL Server in one of the following methods:

  • Transactional.
  • Snapshop.
  • Merge replication.

Q.Can we initiate a external COM object from within SQL?

Answer: Yes we can use the stored procedure sp_OACreate to initiate the external COM object from the T-SQL.

Q.What is a schema? How is it useful in SQL Serers?

Answer: The Schema refers to the overall structure of the database with all related information like users, access privileges, interaction information between the different tables etc. The CREATE SCHEMA is the command that can be used to create the schema in the SQL Server. This when done can be used to re deploy the same database in another system for demonstrative or test purposes. This holds intact the underlying framework over which the database has been built.

Q.What is a write-ahead log?

Answer: The write-ahead log is the logging system that just updates the buffer cache of the database for the transactions and updates the logs and only then the actual changes are incorporated in the actual database. This is the reason why it is called “write ahead”. This helps in maintaining the consistency in the database. This can also be useful in getting the actual database values even in case of failures.

Q.What is the use of check points in the transaction logs?
Answer: The check points are restoration points that indicate the specific state of the database. When there is some failure int he database that is occurring before the next check point, the database can be reverted back to the previous check point and thus the database would still be consistent.

Q.What is a column with identity?

Answer: The column with a defined identity in turn means that there is an unique value that the system assigns to the specific column. This is similar to the AUTONumber property of the Access backend.

Q.What are the different components that constitute the SQL Server architecture?

Answer:  The Logical component consists of the overall database structure definitions, users, groups, access permissions, collations etc.

The Physical component is the one that contains the physically represented form of the database i.e the actual files. There are three types of files:
Primary data files: These contain the links to the other files. This file is the representation of the higher level of the database. (.mdf)
Secondary data files: These contain the files that contain the values and actual data as in database.
Log files: These represent the different types of the logging output of the SQL Server, including the transaction logs.

Q.What are scrollable cursors? How are they created?

Answer: The scrollable cursors are the ones that can get the entire set of rows as single entity, within which all the rows present can be accessed in any order without the open/close of cursor done for every row access. The scrollable cursors are created with the keyword SCROLL added to the CREATE Cursor statements. The scrollable cursors are useful for the access of information from different rows but not for the delete/insert of new rows.

Q.What is RAID? How does it help storage of databases?

Answer: The RAID stands for Redundant Array of Independent Disks. With its own RAID controllers, the RAID implements a fail-safe storage mechanism with its own backup mechanisms. There are different configurations of the RAID that all give us the ACID properties of storage along with other such facilities. This kind of storage will make the SQL Server database to be fail-safe and stable. This can sometimes mean that the backup mechanisms and other such reliability measures can be taken off from the SQL Server level of operations.

Q.How can you identify the version number of the SQL Server installed?

The global variable @@version has the build and version information for the SQL Server and the service packs.

What are the different types of Indexes available in SQL Server?

The simplest answer to this is “Clustered and Non-Clustered Indexes”. There are other types of Indexes what can be mentioned such as Unique, XML, Spatial and Filtered Indexes. More on these Indexes later.

What is the difference between Clustered and Non-Clustered Index?

In a clustered index, the leaf level pages are the actual data pages of the table. When a clustered index is created on a table, the data pages are arranged accordingly based on the clustered index key. There can only be one Clustered index on a table.

In a Non-Clustered index, the leaf level pages does not contain data pages instread it contains pointers to the data pages. There can multiple non-clustered indexes on a single table.

Q.How do you troubleshoot errors in a SQL Server Agent Job?

Answer: Inside SSMS, in Object explorer under SQL Server Agent look for Job Activity Monitor. The job activity monitor displays the current status of all the jobs on the instance. Choose the particular job which failed, right click and choose view history from the drop down menu. The execution history of the job is displayed and you may choose the execution time (if the job failed multiple times during the same day). There would information such as the time it took to execute that Job and details about the error occurred.

Q.What is the default Port No on which SQL Server listens?

Answer:  1433

Q.How many files can a Database contain in SQL Server?How many types of data files exists in SQL Server? How many of those files can exist for a single database?

Answer:  A Database can contain a maximum of 32,767 files.

There are Primarily 2 types of data files Primary data file and Secondary data file(s). There can be only one Primary data file and multiple secondary data files as long as the total # of files is less than 32,767 files.

Q.What is DCL?

Answer: DCL stands for Data Control Language.

Q.What are the commands used in DCL?

Answer:  GRANT, DENY and REVOKE.

Q.What is Fill Factor?

Answer: Fill Factor is a setting that is applicable to Indexes in SQL Server. The fill factor value determines how much data is written to an index page when it is created / rebuilt.

Q.What is the default fill factor value?

Answer: By default the fill factor value is set to 0.

Q.Where do you find the default Index fill factor and how to change it?

Answer: The easiest way to find and change the default fill factor value is from Management Studio, Right click the Server and choose properties. In the Server Properties, choose Database Settings. you should see the default fill factor value in the top section. You can change to a desired value there.

The other of viewing and changing this value is using sp_configure.

Q.What is SQL Profiler. What are the default templates with it?

Answer: SQL Server Profiler is a graphical user interface to SQL Trace for monitoring an instance of the Database Engine or Analysis Services. You can capture and save data about each event to a file or table to analyze later.
Q.What are the DMVs?

Answer: Dynamic Management Views (DMV) return server state information that can be used to monitor the health of a server instance, diagnose problems, and tune performance.

Q.What is the syntax to execute the sys.dm_db_missing_index_details?

Answer: Select * from sys.dm_db_missing_index_details

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