### How to get absolute value in MongoDB

To get the absolute value we can use \$abs operator. \$abs is the arithmetic aggregate operator which returns the absolute value of the number.
Absolute value means it always returns positive value while the number may positive or negative.

Before version of MongoDB 3.2, we can’t use directly on the number like below.

{ \$project: { number: { \$abs: '\$number } }

We needed some calculation as below.

db.Col.aggregate([
{
\$project: { abs_value: { \$abs: { \$subtract: [ 1, 2 ] } } }
}]).
Syntax:

 { \$abs: }

Example: Run the following script which \$subtract will return negative value but \$abs will return the absolute value of subtract.

 db.Col.aggregate([    {      \$project: { abs_value: { \$abs: { \$subtract: [ 1, 2 ] } } }    } ])

OR

 db.ratings.aggregate([    {      \$project: { abs_value: { \$abs: -1 } }    } ])

It will return abs_value =1.0

Note: If the argument field is missing or null it will return null.

{\$abs:-1} result 1
{\$abs:1} result 1

{\$abs:null} result null

### 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>

in drop DropDownList

### How to get first & last day of the previous month

This query will return first day of the previous month

### 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.

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:
Note: Use WITH VALUES to update existing null-able rows.
Example:
Note: WITH VALUES handles the NOT NULL part

### Query to select text only from alphanumeric string in SQL Server

If you want to select text only from alphanumeric string use following query

DECLARE@strVARCHAR(400) DECLARE@expresVARCHAR(50)='%[0-9]%' SET@str='Dilip 007 Singh' WHILEPATINDEX(@expres,@str)> 0 BEGIN SET@str=REPLACE(@str,SUBSTRING(@str,PATIN