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Interview Questions and answers - SQL Server Day 7

Question: What are ACID properties in SQL Server?

Answer: The ACID rules of a transaction in any database ensure the reliability of data in all transactions in the database.

Atomicity
Atomicity shows the ability of the database to assure that either all tasks of a transaction are performed or none of them.

Consistency
Consistency assures that database remains consistent state before the transaction and after the transaction is over.

Isolation
Isolation assures that other operation can't be performed in an intermediate state during a transaction. As a result, transactions that run concurrently appear to be serialized.

Durability
Durability is responsible to notify the transaction is successful; the transaction will persist, not undone. It will survive system failure and the database system has checked the integrity constraints and no need to abort the transaction.
For example, click here 

Question: What is a TRANSACTION in SQL Server?

Answer: Transaction is the collection of T-SQL statements which executes in a single unit. A transaction begins with a specific T-SQL statement and ends when all T-SQL statements execute successfully. If any statements fail then the transaction fails. A transaction has only two types of results success or failure.
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Question: What are COMMIT and ROLLBACK in SQL Server?

Answer: COMMIT statement use to the committed transaction to save changes in the database successfully.
ROLLBACK statement use to stop the current transaction and un-done the changes made by the transaction.
For more details click here 

Question: What is a WITH(NOLOCK) in SQL Server?

Answer: WITH(NOLOCK) used in the SELECT statement to give the priority to select statement. WITH(NOLOCK) unlock the table for a SELECT statement to stop another process.
Example
SELECT * FROM TBL WITH(NOLOCK)

Question: GO command in SQL server?

Answer: GO command indicates the end the SQL statements it is used when there are multiple statements to be executed but sent as a batch.

Question: What is the difference between UNION and UNION ALL in SQL Server?

Answer: UNION operator is used to combining multiple results set into one result set but remove any duplicate rows. Basically, UNION 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 is not removed duplicate rows so it is faster than the UNION operator, if you want to combine multiple results and without duplicate records then use UNION. For more details click here 

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What is difference between UNION and UNION ALL in SQL Server

We use UNION and UNION ALL operator to combine multiple result set into one result set. UNION operator is use to combine multiple result set into one result set but remove any duplicate rows. Basically UNION use to performing a DISTINCT operation across all columns in the result set. UNION operator has extra overhead of removing duplicate rows and sorting result.
UNION ALL operator use to combine multiple result set into one result set but it does not remove any duplicate result. Actually this is not remove duplicate rows so it is faster than UNION operator, if you want to combine multiple results and without duplicate records then use UNION.
Following some rules for using UNION/UNION ALL operator ·Number of column should be same in the query's when you want to combine them. ·Column should be of the same data type. ·ORDER BY clause can be apply on overall result set not within each result set. ·Column name of the final result set will be from the first query.


CREATETABLE #TMP (       ID INT…

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