Skip to main content

Interview Questions and answers - SQL Server Day 2

Question: What is an index in SQL Server?

Answer: Index is responsible to arrange data physically to speed up the query performance. An index is a physical structure containing the pointers of the data. We can create index one or more columns of the table. Creating a relational index on the table is called row-store index it is either clustered or non-clustered index. There are two types of index

1-  Clustered index
2-  Non-clustered index
3-  A new index introduced in SQL Server 2014. “Columnstore index”

Question: What is a cursor in SQL Server?

Answer: Curser is responsible to manipulate data in a set on row by row basis. Actually, curser is the database object used by the application.

Question: Types of an index in SQL Server.

Answer: Types of the index is given below.
  1. Clustered index
  2. Non-clustered index
  3. Columnstore index

Question: What are the constraints in SQL Server?

Answer: Constraints are the rules enforced on data columns on the table. This ensures the accuracy and reliability of the data in the database. Constraints define some conditions that restrict the column to remain true while inserting or updating or deleting data in the column.

Question: Types of constraints in SQL Server?

Answer: Types of constraints is given below.
  1. NOT NULL- This constraint is responsible for a column to confirm that a column cannot have a null value.
  2. DEFAULT – This constraint provides a default value when specified none for this column.
  3. UNIQUE- This constraint ensures that each row for the column has a different value.
  4. PRIMARY KEY- Primary key constraint is a combination of a NOT NULL constraint and a UNIQUE constraint. This constraint ensures that the specific column for a table has a unique identity.
  5. FOREIGN KEY- This constraint responsible to uniquely identified a rows/records in any another database table.
  6. CHECK- The CHECK responsible for enables a condition to check the value being entered into a record

Popular posts from this blog

What is difference between UNION and UNION ALL in SQL Server

We use UNION and UNION ALL operator to combine multiple results set into one result set.
UNION operator is used to combining multiple results set into one result set but removes any duplicate rows. Basically, UNION is used to performing a DISTINCT operation across all columns in the result set. UNION operator has the extra overhead of removing duplicate rows and sorting result.
UNION ALL operator use to combine multiple results set into one result set but it does not remove any duplicate result. Actually, this does not remove duplicate rows so it is faster than the UNION operator. If you want to combine multiple results and without duplicate records then use UNION otherwise UNION ALL is better.
Following some rules for using UNION/UNION ALL operator
1.The number of the column should be the same in the query's when you want to combine them. 2.The column should be of the same data type. 3.ORDER BY clause can be applied to the overall result set not within each result set.
4.Column name of …

Dropdownlist selectedindexchanged event is not firing

<asp:DropDownList ID="ddlSource" runat="server" DataSourceID="SqlDataSource1" DataTextField="vcSuplierNm" ViewStateMode="Enabled DataValueField="vcSuplierCode" EnableViewState="true" AppendDataBoundItems="true" OnSelectedIndexChanged="ddl_OnSelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>

Add property ViewStateMode="Enabled" and EnableViewState="true"
in drop DropDownList

Remove special characters from string in SQL server

I faced many times an issue to remove special characters from a string. Suppose you are working on searching concept and you have to remove the special characters from search string due to query performance, there are many solution are available but T-SQL is easily resolved this issue.
Following query may help you to resolve your issue.

DECLARE@strVARCHAR(400) DECLARE@expresVARCHAR(50)='%[~,@,#,$,%,&,*,(,),.,!]%' SET@str='(remove) ~special~ *characters. from string in sql!' WHILEPATINDEX(@expres,@str)> 0 BEGIN SET@str=Replace(REPLACE(@str,SUBSTRING(@str,PATINDEX(@expres,@str), 1 ),''),'-',' ') END SELECT@str



Add day to ISODate in MongoDB

We can use $add operator to add days in ISODate in mongodb, $add is the Arithmetic Aggregation Operator which adds number and date in mongodb.
Syntax:

{ $add: [ <expression1>, <expression2>, ... ] }

Note:  If one of the argument is date $add operator treats to other arguments as milliseconds to add to the date.
Example: Suppose we have a Test collection as below.

{"Title" : "Add day to ISODate in MongoBD","CreatedDate" : ISODate("2016-07-07T08:00:00.000Z")}

Query to add 2 days in CreatedDate

db.Test.aggregate([      { $project: { Title: 1, AddedDate: { $add: [ "$CreatedDate", 2*24*60*60000 ] } } }    ])

Result:

{ "_id" : ObjectId("579a1567ac1b3f3732483de0"), "Title" : "Add day to ISODate in MongoBD", "AddedDate" : ISODate("2016-07-09T08:00:00.000Z") }

Note: As mentioned in above note we have to convert days in millisecond because $add operator treat to other arg…

Remove special character from string in MongoDB

Problem: Suppose wehave a collection and one field is type string contains some special character (like !@#$%) and we don’t want these special character.
Solution: We can easily remove the special character from field using script “replace(/[^a-zA-Z 0-9 ]/g, '')” in our query.  How can we remove special character from string using this script please see following example.
Example: Suppose we have a collection “EduSurvey “where we are collecting information from institutions.

{Name:"JB institute”, About:"This is good one collage for MBA", Information:"This $%%institute ##has good faculty etc$$"}
{Name:"MK institute”, About:"This is good one collage for MCA", Information:"This$$%# is the dummy text12"}
{Name:"MG institute”, About:"This is good one collage for B,Tech", Information:"This# institute@ has&* good infrastructure"}

Did you notice Information fields contains some special character so we…

$group (aggregation) in MongoDB

IF we want to group document by specific expression and want to output for each distinct grouping of document here we have to use $group. IF you familiar with Relational Database like SQL Server, It's work same like GROUP BY clause.
Output document contains the _id field which contains the distinct group by key also output document contains computed fields which grasp the value of some accumulator expression grouped by the _id.
Syntax:

{ $group: { _id: <expression>, <field1>: { <accumulator1> : <expression1> }, ... }

Accumulator Operator:
$num : It's returns sum of the numeric value. It can be use in $project also in mongodb 3.2 version.
$avg  : It's returns the average of numeric values. It can be use in $project also in mongodb 3.2 version.
$first : It's returns a value from the first document for each group.
$last : It's returns a value from the first document for each group.
$max : It's returns the highest expression value for each group.…

Add a column, with a default value, to an existing table in SQL Server

You can do it by edit of table design, if you want do it with query see following.
Syntax:
ALTERTABLE{TABLENAME} ADD{COLUMNNAME}{TYPE}{NULL|NOTNULL} CONSTRAINT{CONSTRAINT_NAME}DEFAULT{DEFAULT_VALUE} [WITH VALUES]
Note: Use WITH VALUES to update existing null-able rows.
Example:
ALTERTABLEMyTable ADDMyTableTypeIDINTNOTNULL CONSTRAINTConstraint_MyTableTypeIDDEFAULT0 GO
Note: WITH VALUES handles the NOT NULL part
ALTERTABLEMyTable ADDMyTableTypeIDINT CONSTRAINTConstraint_MyTableTypeIDDEFAULT

Merge and Merge join transformation in SSIS