Naver Frequently Asked SQL Server Interview Questions Answers

What Are The Operating Modes In Which Database Mirroring Runs?

Database Mirroring runs in 2 operating modes High-Safety Mode and High-Performance Mode.

What Is The Difference Between The 2 Operating Modes Of Database Mirroring?

High-Safety Mode is to ensure that the Principal and Mirrored database are synchronized state, that is the transactions are committed at the same time on both servers to ensure consistency, but there is/might be a time lag.

High-Performance Mode is to ensure that the Principal database run faster, by not waiting for the Mirrored database to commit the transactions. There is a slight chance of data loss and also the Mirrored database can be lagging behind (in terms being up to date with Principal database) if there is a heavy load on the Mirrored Server.

What Is Fill Factor?

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.

What Is The Default Fill Factor Value?

By default the fill factor value is set to 0.

Where Do You Find The Default Index Fill Factor And How To Change It?

The easiest way to find and change the default fill factor value is from Management Studio, right-click the SQL 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 and click OK to save the changes. The other option of viewing and changing this value is using

What Is A System Database And What Is A User Database?

System databases are the default databases that are installed when the SQL Server is installed. Basically there are 4 system databases: Master, MSDB, TempDB and Model. It is highly recommended that these databases are not modified or altered for smooth functioning of the SQL System.

A user database is a database that we create to store data and start working with  the data.

Naver Frequently Asked SQL Server Interview Questions Answers

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?

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 thetotal # of files is less than 32,767 files

What Is Dcl?

DCL stands for Data Control Language.

What Are The Commands Used In Dcl?

GRANT, DENY and REVOKE.

What Are The Different Authentication Modes In Sql Server And How Can You Change Authentication Mode?

SQL Server has 2 Authentication modes: Windows Authentication and SQL Server and Windows Authentication mode also referred as Mixed Mode.

What Are The Differences In Clustering In Sql Server 2005 And 2008 Or 2008 R2?

On SQL Server 2005, installing SQL Server failover cluster is a single step process whereas on SQL Server 2008 or above it is a multi-step process. That is, in SQL Server 2005, the Installation process itself installs on all of the nodes (be it 2 nodes or 3 nodes). In 2008 or above this has changed, we would need to install separately on all the nodes. 2 times if it is a 2 node cluster or 3 times in a 3 node cluster and so on.

What Is Meant By Active – Passive And Active – Active Clustering Setup?

An Active – Passive cluster is a failover cluster configured in a way that only one cluster node is active at any given time. The other node, called as Passive node is always online but in an idle condition, waiting for a failure of the Active Node, upon which the Passive Node takes over the SQL Server Services and this becomes the Active Node, the previous Active Node now being a Passive Node.

An Active –Active cluster is a failover cluster configured in a way that both the cluster nodes are active at any given point of time. That is, one Instance of SQL Server is running on each of the nodes always; when one of the nodes has a failure, both the Instances run on the only one node until the failed node is brought up (after fixing the issue that caused the node failure). The instance is then failed over back to its designated node.

List Out Some Of The Requirements To Setup A Sql Server Failover Cluster.?

Virtual network name for the SQL Server, Virtual IP address for SQL Server, IP addresses for the Public Network and Private Network(also referred as Hearbeat) for each node in the failover cluster, shared drives for SQL Server Data and Log files, Quorum Disk and MSDTC Disk.

On A Windows Server 2003 Active – Passive Failover Cluster, How Do You Find The Node Which Is Active?

Using Cluster Administrator, connect to the cluster and select the SQL Server cluster.  Once you have selected the SQL Server group, in the right hand side of the console, the column“Owner” gives us the information of the node on which the SQL Server group is currently active.

How Do You Open A Cluster Administrator?

From Start -> Run and type CluAdmin (case insensitive) and the Cluster Administrator console is displayed OR you can also go to Start -> All programs -> Administrative Tools -> Cluster Administrator.

Due To Some Maintenance Being Done, The Sql Server On A Failover Cluster Needs To Be Brought Down. How Do You Bring The Sql Server Down?

In the Cluster Administrator, rick click on the SQL Server Group and from the popup menu item choose Take Offline.

What Are The Different Ways You Can Create Databases In Sql Server?

T-SQL; Create Database command.
Using Management Studio
Restoring a database backup
Copy Database wizard

When Setting Replication, Can You Have Distributor On Sql Server 2005, Publisher On Sql Server 2008?

No you cannot have a Distributor on a previous version than the Publisher.

When Setting Replication, Is It Possible To Have A Publisher As 64 Bit Sql Server And Distributor Or Subscribers As A 32 Bit Sql Server.

Yes it is possible to have various configurations in a Replication environment.

What Is The Difference Between Dropping A Database And Taking A Database Offline?

Drop database deletes the database along with the physical files, it is not possible to bring back the database unless you have a backup of the database. When you take a database offline, you the database is not available for users, it is not deleted physically, it can be brought back online.

Which Autogrowth Database Setting Is Good?

Setting an autogrowth in multiples of MB is a better option than setting autogrowth in percentage (%).

What Are The Different Types Of Database Compression Introduced In Sql Server 2008?

Row compression and Page compression.

What Are The Different Types Of Upgrades That Can Be Performed In Sql Server?

In-place upgrade and Side-by-Side Upgrade.

What Are The Recovery Models For A Database?

There are 3 recovery models available for a database. Full, Bulk-Logged and Simple are the three recovery models available.
What Is The Importance Of A Recovery Model?

Primarily, recovery model is chosen keeping in view the amount of data loss one can afford to. If one expects to have minimal or no data loss, choosing the Full recovery model is a good choice. Depending on the recovery model of a database, the behavior of database log file changes. I would recommend you read more material on log backups and log file behavior and so on to understand in depth.

What Is Replication?

Replication is a feature in SQL Server that helps us publish database objects and data and copy (replicate) it to one or more destinations. It is often considered as one of the High-Availability options. One of the advantages with Replication is that it can be configured on databases which are in simple recovery model.

What The Different Types Of Replication And Why Are They Used?

There are basically 3 types of replication: Snapshot, Transactional and Merge Replication. The type of Replication you choose, depends on the requirements and/or the goals one is trying to achieve.For example Snapshot Replication is useful only when the data inside the tables does not change frequently and the amount of data is not too large, such as a monthly summary table or a product list table etc. Transactional Replication would useful when maintaining a copy of a transactional table such as sales order tables etc. Merge Replication is more useful in case of  remote / distributed systems where the data flow can be from multiple sites, for example sales done at a promotional events which might not be connected to the central servers always.

What The Different Components In Replication And What Is Their Use?

The 3 main components in Replication are Publisher, Distributor and Subscriber. Publisher is the data source of a publication. Distributor is responsible for distributing the database objects to one or more destinations. Subscriber is the destination where the publishers data is copied / replicated.

What The Different Topologies In Which Replication Can Be Configured?

Replication can be configured in any topology depending keeping in view of the complexity and the workload of the entire Replication. It can be any of the following

Publisher, Distributor and Subscriber on the same SQL Instance. Publisher and Distributor on the same SQL Instance and Subscriber on a separate Instance. Publisher,Distributor and Subscriber on individual SQL Instances.

If You Are Given Access To A Sql Server, How Do You Find If The Sql Instance Is A Named Instance Or A Default Instance?

I would go to the SQL Server Configuration Manager.In the left pane of the tool, I would select SQL Server Services, the right side pane displays all of the SQL Server Services / components that are installed on that machine. If the Service is displayed as (MSSQLSERVER), then it indicates it is a default instance, else there will be the Instance name displayed.

What Is Sub-query? Explain Properties Of Sub-query?

Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of parentheses. Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.

A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a resultset. Meaning a subquery SELECT statement can standalone and is not depended on the statement in which it is nested. A subquery SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery can be used anywhere an expression can be used.

What Are Different Types Of Join?

Cross Join
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.

Inner Join
A join that displays only the rows that have a match in both joined tables is known as inner Join. This is the default type of join in the Query and View Designer.

Outer Join
A join that includes rows even if they do not have related rows in the joined table is an Outer Join. You can create three different outer join to specify the unmatched rows to be included
• Left Outer Join: In Left Outer Join all rows in the first-named table i.e. “left” table, which appears leftmost in the JOIN clause are included. Unmatched rows in the right table do not appear.
• Right Outer Join: In Right Outer Join all rows in the second-named table i.e. “right” table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
• Full Outer Join: In Full Outer Join all rows in all joined tables are included, whether they are matched or not.

Self Join
This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company has a hierarchal reporting structure whereby one member of staff reports to another. Self Join can be Outer Join or Inner Join.

What Are Primary Keys And Foreign Keys?

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.

Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.

What Is Cursor?

Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.

In order to work with a cursor we need to perform some steps in the following order

• Declare cursor
• Open cursor
• Fetch row from the cursor
• Process fetched row
• Close cursor
• Deallocate cursor

What Is Collation?

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, character types and character width.

What Is Difference Between Function And Stored Procedure?

UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be. UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables. Inline UDF’s can be thought of as views that take parameters and can be used in JOINs and other Rowset operations.

What Is User Defined Functions? What Kind Of User-defined Functions Can Be Created?

User-Defined Functions allow defining its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.

Different Kinds of User-Defined Functions created are

Scalar User-Defined Function
A Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages. You pass in 0 to many parameters and you get a return value.

Inline Table-Value User-Defined Function
An Inline Table-Value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.

Multi-statement Table-Value User-Defined Function
A Multi-Statement Table-Value user-defined function returns a table and is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a TSQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored procedure which can also return record sets.

What Is Identity?

Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers; the value of this cannot be controlled. Identity/GUID columns do not need to be indexed.

What Is De-normalization?

De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

What Is Stored Procedure?

A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_helpdb, sp_renamedb, sp_depends etc.

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; 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 Is View?

A simple view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. 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. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.

What Is Index?

An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes; they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.