Before SQL Server 2017 (SQL Server 2014 below), concatenating rows of strings into one column could be done using the STUFF function that combines with FOR XML PATH. However, in my opinion, it's quite messy. In this article, we'll explore SQL's STRING_AAG function and see how we can concatenate rows of strings into one column string using a separator.

The examples provided will work with SQL Server 2017 and later.

Ok, let's get started.

What's SQL's STRING_AAG Function?
    It is an aggregate function that concatenates strings into a single line separated by a separator.
    The separator is not appended to the end of the result string.
    This function was introduced into SQL Server 2017 and later.

Syntax
STRING_AGG(string expression, separator) [order clause]
    The string expression could be any type.
        It can be converted into VARCHAR or NVARCHAR during concatenation.
        Non-string types are converted to NVARCHAR types.
    The separator is used as a separator for the concatenated strings.
        It can be literal or variable. Just remember it doesn't add itself at the end of the result string.
    The order clause is the sort order of the result string using the WITHIN GROUP clause.

Syntax of WITHIN GROUP
WITHIN GROUP (ORDER BY expression [ASC | DESC])
    The expression can be used for sorting results; only one expression is allowed per query.
        The default order is ascending.

Examples
Before we show examples, the AdventureWorks database will be used for the first of our samples.
Using STRING_AGG First Example

To have an overview, the [Sales].[SalesOrderHeader] under the AdventureWorks database does have a [SalesOrderNumber] column.

And we wanted to show the list of different sales-order-number per customer by using the STRING_AGG function.

Ok, let's see the examples below.

SELECT CustomerID as [Customer ID],
       COUNT(CustomerID) as [Number Of Sales Order] ,
       STRING_AGG([SalesOrderNumber], ',') as [Sales Order List]
FROM [AdventureWorks2019].[Sales].[SalesOrderHeader]
GROUP BY CustomerID

As you can see, with the query that we have we did get the [CustomerID] column as our reference for a particular customer.

Then by knowing the number of its records, we can show the different sales-order numbers per record.

But, of course, using the STRING_AGG.

That's why we can come up with the query above.

Let's see the output below.

Output

Now, for us to appreciate the WITHIN GROUP syntax when using STRING_AGG.

Let's look at the example below.

SELECT CustomerID as [Customer ID],
       COUNT(CustomerID) as [Number Of Sales Order],
       STRING_AGG([SalesOrderNumber], ',')
       WITHIN GROUP (ORDER BY [SalesOrderNumber] DESC)
       as [Sales Order List]
FROM [AdventureWorks2019].[Sales].[SalesOrderHeader]
GROUP BY  CustomerID

Output

Now, let's try to see the difference between the two outputs.

Output Difference

Using STRING_AGG Second Example
In this section, I will try to give another example. The idea here is to get all the phone numbers of a particular customer; it seems easy, right?
Yap, let's show the code now, and let's create the table structure.

Note: We'll use a local temporary table to avoid tabl structure complexities.

Build the structure first.
-- 1. Let's create the tables needed.
IF OBJECT_ID(N'tempdb..#Customers') IS NOT NULL
BEGIN
    DROP TABLE #Customers
END

CREATE TABLE #Customers(
    Id int,
    FirstName nvarchar(50),
    LastName nvarchar(50)
)

IF OBJECT_ID(N'tempdb..#CustomersPhone') IS NOT NULL
BEGIN
    DROP TABLE #CustomersPhone
END

CREATE TABLE #CustomersPhone(
    PhoneId int,
    UserId int,
    PhoneNumber nvarchar(50)
)

Second, let's put some data on it.
-- 2. Let's put some data on it.

INSERT INTO #Customers VALUES
(1, 'Peter', 'Scott'),
(2, 'Mark', 'Tom')

INSERT INTO #CustomersPhone
VALUES
(1, 1, '+63 895 789 5751'),
(2, 1, '+63 795 689 5752'),
(3, 1, '+63 695 589 5753'),
(1, 2, '+63 915 739 5651'),
(2, 2, '+63 917 649 5552'),
(3, 2, '+63 095 559 5453');

Third, let's create a query that will show the customer's name, the number of phones they have, and their phone list separated by a comma.

-- 3. Let's show the number of phone and phone list a customer have.
SELECT CONCAT(C1.[LastName], ', ', C1.[FirstName]) as [FullName],
       COUNT(C1.Id) as [Total Phone Number],
       STRING_AGG (P1.[PhoneNumber], ',') as [Phone List]
FROM #CustomersPhone P1
INNER JOIN #Customers C1 ON P1.UserId = C1.Id
GROUP BY C1.Id, C1.[LastName], C1.[FirstName]

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SQL Server 2012 introduced two new string functions: CONCAT and FORMAT. The CONCAT string function concatenates two or more strings into one string. CONCAT takes string arguments as input and concatenates these string inputs into a single string. It requires a minimum of two strings as input, otherwise it raises a compile time error. Here all arguments (inputs) are converted into a string type implicitly. A null value is implicitly converted into an empty string.
 
Syntax
CONCAT ( stringvalue1, stringvalue2 ,…, stringvalueN )
 
Argument / parameter
String Value:  A String value to concatenate with the other.
 
Example
--Example of simple string concatenation
SELECT CONCAT('Hi, ', 'I AM ', 'Peter' )

--Output
-- Hi, I AM Peter
--Example of NULL  string concatenation
SELECT CONCAT('Hello ', NULL, 'World' );

--Output
-- Hello World
--Example of other Data type  concatenation with string

SELECT CONCAT('Date : ', CAST(GETDATE() AS DATE));
--Date : 2013-09-25
SELECT CONCAT(123 + '.' + 45  );

--123.45

If all arguments are null then this function returns a string of type VARCAHR (1). The return type of this function depends on the arguments.
    If an argument is a SQL type NVARCHAR (MAX) or SQL CLR system type then the return type of this function is NVARCHAR (MAX)
    If an argument is VARBINARY (MAX) or VARCHAR (MAX) then the result type is VARCHAR (MAX) and if one of argument is NVARCHAR then the output is NVARCHAR (MAX).
    If an argument is NVARCHAR (<= 4000) than result  type is NVARCHAR (<= 4000)
    All other cases result in a type of VARCHAR (<=8000).
    When the length of the arguments are less than 4000 for NVARCHAR or less than 8000 for VARCHAR, implicit conversions can affect the length of the result type.

Other data types, like INT and FLOAT have different lengths when converted to a string. For example, an INT data type length is 12 when converted to a string, so the result of concatenating two integers has a length of 24.
 
FORMAT
The FORMAT string function returns a string formatted value with the specified format and culture (this is optional). We can use the FORMAT function for locale-aware formatting of a date and time and number values as a string.
 
Syntax
FORMAT (Value, Format , Culture)
 
Arguments / parameters
Value -  value in supported data type to format
Format - NVARCHAR format pattern. This argument must contain a valid .NET framework format string. Composite formatting is not supported. It is either a standard format string or a pattern for custom characters for dates and numeric values.
Culture - NVARCHAR Type specifies a culture.

A culture argument is optional, if we are not providing the culture value then the language of current session is used. The language can be set implicitly or explicitly (using a SET LANGUAGE statement). The culture argument accepts all cultures supported by the .NET Framework. It is not limited to the languages supported by SQL Server. If the culture argument is invalid then the Format string function throws an error.

Please refer to http://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo(v=vs.80).aspx to learn more about cultures supported by the .NET Framework.
 
Return Type is NVARCHAR or NULL
A FORMAT string function always returns NULL for an error when the culture is invalid. For the argument value, supported data types are numeric (like TINYINT, SMALLINT, INT, BIGINT, FLOAT, NUMERIC, DECIMAL, SMALLMONEY, MONEY and REAL) and date and time data type (like DATE, TIME, SMALLDATETIME, DATETIME, DATETIME2 and DATETIMEOFFSET). This function will not be remote and it depends on the presence of the Common Language Runtime (CLR).
 
Example
--Example of simple FORMAT string function
DECLARE @mydate DATETIME = '09/25/2013';
SELECT FORMAT ( @mydate, 'd', 'en-US' ) AS 'US Format'
,FORMAT ( @mydate, 'd', 'en-gb' ) AS 'GB Format'
--Output
--US Format         GB Format
----------------  -------------
--09/25/2013         25/09/2013
DECLARE @mydate DATETIME = '09/25/2013';
SELECT FORMAT ( @mydate, 'D', 'en-US' ) AS 'US Format'
,FORMAT ( @mydate, 'D', 'en-gb' ) AS 'GB Format'

--Output
--US Format GB Format
--Wednesday,September 25, 2013      25 September 2013  
--Example of custom formatting string
DECLARE @mydate DATETIME = '09/25/2013';

SELECT FORMAT ( @mydate, 'dd/MM/yyyy', 'en-US' )
--Output
--25/09/2013

SELECT FORMAT(555230655,'###-##-####')
--Output
--555-23-0655
--Example of formatting numeric type
SELECT FORMAT (8875.644 , 'C' ,  'en-US' ) AS 'Currency Format1'
,FORMAT (8875.644 , 'C0',  'en-US' ) AS 'Currency Format2'

Output
-- Currency Format1         Currency Format2      
  $8,875.64                        $8,876
 
These two newly introduced functions are very useful. The CONCAT string function is useful to concatenate two or more values and values of one or more data types. The FORMAT string function gets a formatted value with the specified format and optional culture.

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In this article, you will learn how to Format Dates in SQL Server.
Here we will use the “FORMAT” function to format a date in SQL Server

Prerequisites

    Install SQL Server
    Install SQL Server Management Studio (SSMS)

For the above prerequisites, you can follow the article How to Install SQL Server and SQL Server Management Studio (SSMS)

Currently, I have installed SQL Server 2019 and SQL Server Management Studio 18.10 (SSMS) on my windows 11 machine.
Built-in function in SQL Server to get the DateTime value in a specific format

By using some built-in function in SQL Server we can get the DateTime value in a specific format.

For example,

GETDATE()
It returns server DateTime in “YYYY-MM-DD HH:mm:ss.fff” format.

SELECT GETDATE() AS [GETDATE()]
Result:-2022-06-09 12:28:37.787

GETUTCDATE()

It returns DateTime in GMT.

SELECT GETUTCDATE() AS [GETDATE()];
Result:-2022-06-09 07:10:54.350

SYSDATETIME()
It returns the server’s DateTime

SELECT SYSDATETIME() AS [GETDATE()];
Result:2022-06-09 12:41:46.8713228

SYSDATETIMEOFFSET()

It returns the server’s DateTime with time zone in which SQL Server instance is running.

SELECT SYSDATETIMEOFFSET() AS [GETDATE()];
Result:2022-06-09 12:42:15.7936382 +05:30

SYSUTCDATETIME()
It returns server DateTime in GMT.

SELECT SYSUTCDATETIME() AS [GETDATE()];
Result:2022-06-09 07:12:54.4664815

CURRENT_TIMESTAMP
It returns current DateTime of the server.

SELECT CURRENT_TIMESTAMP AS [GETDATE()];
Result:2022-06-09 12:43:40.650

After the CONVERT function, SQL Server added a function (FORMAT) to handle date formatting, giving us a new way to format dates in SQL Server.

To format the date and time data types from a date column (Date, DateTime, etc. Data type) in a table or a variant such as GETDATE(), use the FORMAT function.
Date Format with FORMAT Function

We have many ways to format dates as given below
DD/MM/YYYY
SELECT FORMAT (getdate(), 'dd/MM/yyyy ') as date;
Result:09/06/2022


DD/MM/YYYY, HH:MM:SS
SELECT FORMAT (getdate(), 'dd/MM/yyyy, hh:mm:ss ') as date;
Result:09/06/2022, 04:56:44

DDDD,MMMM,YYYY
SELECT FORMAT (getdate(), 'dddd, MMMM, yyyy') as date;
Result:Thursday, June, 2022

MMM DD YYYY
SELECT FORMAT (getdate(), 'MMM dd yyyy') as date;
Result:Jun 09 2022

MM.DD.YY
SELECT FORMAT (getdate(), 'MM.dd.yy') as date;
Result:06.09.22


MM-DD-YY
SELECT FORMAT (getdate(), 'MM-dd-yy') as date;
Result:06-09-22

HH:MM:SS TT
SELECT FORMAT (getdate(), 'hh:mm:ss tt') as date;
Result:05:17:37 PM

MM/DD/YYYY (Standard: USA)
SELECT FORMAT (getdate(), 'd','us') as date;
Result:06/09/2022

YYYY-MM-DD HH:MM:SS TT
SELECT FORMAT (getdate(), 'yyyy-MM-dd hh:mm:ss tt') as date;
Result:2022-06-09 05:18:55 PM

YYYY.MM.DD HH:MM:SS T
SELECT FORMAT (getdate(), 'yyyy.MM.dd hh:mm:ss t') as date;
Result:2022.06.09 05:19:53 P

DDDD,MMM,YYYY in Spanish
SELECT FORMAT (getdate(), 'dddd, MMMM, yyyy','es-es') as date;
Result:jueves, junio, 2022

DDDD DD, MMMM,YYYY in Japanese
SELECT FORMAT (getdate(), 'dddd dd, MMMM, yyyy','ja-jp') as date;
Result:木曜日 09, 6月, 2022

Date Format with Culture
We can get regional formatting by using the culture option as shown below:

English-USA
SELECT FORMAT (getdate(), 'd', 'en-US') as date;
Result:6/10/2022

French-France
SELECT FORMAT (getdate(), 'd', 'fr-FR') as date;
Result:10/06/2022

French - Belgium
SELECT FORMAT (getdate(), 'd', 'fr-BE') as date;
Result:10-06-22

French - Canada
SELECT FORMAT (getdate(), 'd', 'fr-CA') as date;
Result:2022-06-10

Danish - Denmark
SELECT FORMAT (getdate(), 'MM.dd.yy') as date;
Result:06.10.22

Dari - Afghanistan
SELECT FORMAT (getdate(), 'd', 'prs-AF') as date;
Result:1401/3/20


Simplified Chinese
SELECT FORMAT (getdate(), 'd', 'zh-CN') as date;
Result:2022/6/10

Divehi - Maldives
SELECT FORMAT (getdate(), 'd', 'dv-MV') as date;
Result:10/06/22

Bosnian Latin
SELECT FORMAT (getdate(), 'd', 'bs-Latn-BA') as date;
Result:10. 6. 2022.

isiXhosa / Xhosa - South Africa
SELECT FORMAT (getdate(), 'd', 'xh-ZA') as date;
Result:2022-06-10

Hungarian - Hungary
SELECT FORMAT (getdate(), 'd', 'hu-HU') as date;
Result:2022. 06. 10.

Spanish - Bolivia
SELECT FORMAT (getdate(), 'd', 'es-bo') as date;
Result:10/6/2022

Here is a list of all CultureInfo codes along with country names and language.

As you saw above, we have used a lot of options for date and time formatting, which are detailed below,

• hh - this is the hour from 01-12
• HH - this is the hour from 00-23
• mm - this is the minute from 00-59
• ss - this is the second from 00-59
• dd - this is day of month from 01-31
• dddd - this is the day spelled out
• MM - this is the month number from 01-12
• MMM - month name abbreviated
• MMMM - this is the month spelled out
• yy - this is the year with two digits
• yyyy - this is the year with four digits
• tt - this shows either AM or PM
• d - this is day of month from 1-31 (if this is used on its own it will display the entire date)
• us - this shows the date using the US culture which is MM/DD/YYYY

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This article will explain to you how exactly you need to configure TLS 1.2 as a default protocol and setup SMTP O365 migration with Database mail using SQL 2012 and above versions for Windows Server 2012 and above.

Common SMTP exceptions we usually faced
The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 2. Exception Message: Cannot send mails to mail server. (Failure sending mail.). )

Just follow the steps. The below steps are verified, proven, and compatible with the below servers and SQL versions,
    Windows Server 2012 R2 – SQL Server 2014 SP3
    Windows Server 2012 R2 – SQL Server 2012
    Windows Server 2016 – SQL Server 2016
    Windows Server 2016 – SQL Server 2017 and above.

Step 1
Check if your .NET framework is 4.6 or above, especially for SQL 2014/2016 version. Otherwise, install the latest .Net version. To verify the current version, open PowerShell, and run as administrator. Copy and execute the below command

reg query "HKLM\SOFTWARE\Microsoft\Net Framework Setup\NDP\v4" /s

Step 2
Check if .NET 3.5 was installed (You can skip this installation for SQL Server 2017, but the .Net framework installation must be .Net 4.8 or above)

Powershell command to list out the installed.NET versions - Run as admin
gci 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP’ -recurse | gp -name Version -EA 0 | where { $_.PSChildName -match ‘^(?!S)\p{L}’} | select PSChildName, Version

If not installed, either install 3.5 or place a config file in Binn folder
C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Binn\DatabaseMail.exe.config

Place the XML content
<?xml version="1.0" encoding="utf-8" ?>
    <configuration>
        <startup useLegacyV2RuntimeActivationPolicy="true">
            <supportedRuntime version="v4.0"/>
            <supportedRuntime version="v2.0.50727"/>
        </startup>
    </configuration>

Save file as DatabaseMail.exe.config, with UTF-8 and saved in config format
MSSQL13/14/15 – Version depends on the SQL server installed. Forex: MSSQL13 – 2014 and MSSQL14-2016

Step 3
Install the Database mail advanced configuration. Execute the first query
sp_configure 'show advanced options', 1;
GO
RECONFIGURE;
GO
sp_configure 'Database Mail XPs', 1;
GO
RECONFIGURE
GO

Step 4
Enable the Windows firewall in the Azure portal under networking for VM
Add a rule in Inbound port rules and Outbound port rules with the highest priority by enabling the recommended port 587 with TCP protocol

Step 5
Enable the TLS 1.2 by adding/updating the registry Keys under Regedit. Click on start and type registry editor, run as admin, go to the respective Path and add the key(folder) and (DWord 32-bit) value

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727]
"DefaultSecureProtocols"=dword:00000001
"SchUseStrongCrypto"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v2.0.50727]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001

[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\.NETFramework\\v4.0.30319]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001

[HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\Microsoft\\.NETFramework\\v4.0.30319]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\SSL 2.0\\Client]
"DisabledByDefault"=dword:00000001

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.2\\Client]
"DisabledByDefault"=dword:00000000
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.2\\Server]
"DisabledByDefault"=dword:00000000
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp]
"DefaultSecureProtocols"=dword:00000800

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp]
"DefaultSecureProtocols"=dword:00000800

NOTE: Make sure you add only the pre-defined registry keys. Any typo error will stop the registry functions instantly. Copy and paste exactly the same.

Step 6
Configure SQL Database mail with account Name, Email-address [email protected], Server Name, PORT, Enable SSL, and Basic Auth

Step 7
Restart the machine and try the Database mail. If this does not work, add the below registry keys

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\SSL 2.0\\Client]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\SSL 2.0\\Server]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\SSL 3.0\\Client] #apply only if the registry key (SSL 3.0) is present
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\SSL 3.0\\Server] #apply only if the registry key(SSL 3.0) is present
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.0\\Client]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.0\\Server]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.1\\Client]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\SecurityProviders\\SCHANNEL\\Protocols\\TLS 1.1\\Server]
"DisabledByDefault"=dword:00000001
"Enabled"=dword:00000000

Step 8
Restart again and Check if the TLS 1.2 is enabled through PowerShell. Copy, paste, and execute

$key = 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client\'
if (Test-Path $key) {
  $TLS12 = Get-ItemProperty $key
  if ($TLS12.DisabledByDefault -ne 0 -or $TLS12.Enabled -eq 0) {
    Throw "TLS 1.2 Not Enabled"
  }
  else{
 "TLS is enabled"
  }
}

Step 9
Execute the PowerShell and check if the email has triggered. Change values for $From - (Domain Account), $To - (User Account) , $Email.Credentials - (Domain Account and Password) variables
#Email Information
$From = "[email protected]"
$To = "[email protected]"
$Subject = "Test authenticated O365 smtp email"
$Body = "Test smtp email sent through Office 365's smtp relay."
#SMTP Relay Settings
$SMTP = "smtp.office365.com"
$Port = 587
$Email = New-Object Net.Mail.SmtpClient($SMTP, $Port)
$Email.EnableSsl = $true
$Email.Credentials = New-Object System.Net.NetworkCredential("[email protected]", "Add Password")
$Email.Send($From, $To, $Subject, $Body)

Step 10
Send test email from step-6 Database mail

Step 11
Execute the below SQL query and verify your email has been sent
select top 10 * from msdb.dbo.sysmail_sentitems order by send_request_date desc;
select top 10 * from msdb.dbo.sysmail_event_log order by log_date desc;

Step 12
If you are still struggling with the email, then the issue is probably in the Exchange Center. To resolve that, log in to the O365 and go to the Microsoft 365 Admin Center, select Users and follow the steps

Go to the Active User([email protected]) and select Manage Email Apps under the Mail tab and enable IMAP, POP, and Authenticated SMTP and execute the Powershell or Database mail test email and see the magic :-)

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In some cases, using the CASE statement can lead to numerous conditions. You may agree or not; these multiple conditions will look extensive and lengthy in some situations. Moreover, it can be challenging to maintain because of its complexity.

That's why in this post, we'll explore CHOOSE function. It helps developers have a better alternative to the CASE statement when simplifying lengthy conditions.
What's CHOOSE Function in SQL Server?

    Introduced in SQL Server 2012
    A function returns a specific value from a list based on its number index.
    It looks like an array, but the index starts from 1.

Syntax
CHOOSE (INDEX, VALUE1, VALUE2, VALUE3, VALUE4...)

Index
This is the element's position we seek in the output. Remember that CHOOSE doesn't use a zero-based index strategy (meaning the first item starts with 1). If in case the index is not an integer, SQL converts it to an integer otherwise returns NULL.

Values
It is a comma-separated list of any data type. Returns an item based on the index specified in the first(index) parameter.
Examples
 
1. Item index starts at 1
--Let's just say we wanted to list our favorite programming languages

--output: JavaScript
SELECT CHOOSE (1, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: Python
SELECT CHOOSE (2, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C#
SELECT CHOOSE (3, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C++
SELECT CHOOSE (4, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C
SELECT CHOOSE (5, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

Output

2. When CHOOSE Function Returns NULL
--output: NULL
SELECT CHOOSE (0, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

--output: NULL
SELECT CHOOSE (6, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

Output

If we have passed the index outside the value list range, you'll be getting NULL as the return value.

3. Using Float or Decimal as Index Values
--output: NULL
SELECT CHOOSE (0.10, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: JavaScript
SELECT CHOOSE (1.10, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: Python
SELECT CHOOSE (2.23, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C#
SELECT CHOOSE (3.9923423, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C++
SELECT CHOOSE (4.7412122, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C
SELECT CHOOSE (5, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: NULL
SELECT CHOOSE (6.636, 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

Output

In our example above, we have seen that once we have passed a float or decimal data type, the value is implicitly converted into an integer as long as it's not int. We'll have the same output as from the first two examples.

4. Using String as Index-values
In this section, you'll see that we can still pass a string that has an integer value.

Let's see an example below.

--Let's just say we wanted to list our favorite programming languages
-- This time around, we'll use string but with a correct integer index
--output: JavaScript
SELECT CHOOSE ('1', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: Python
SELECT CHOOSE ('2', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C#
SELECT CHOOSE ('3', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C++
SELECT CHOOSE ('4', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: C
SELECT CHOOSE ('5', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

Output

However, if we pass a non-integer value like an alphanumeric value or decimal value, it will throw an exception.

Let's see an example below.

--output: exception
SELECT CHOOSE ('One', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'
--output: exception
SELECT CHOOSE ('1.15', 'JavaScript','Python', 'C#', 'C++', 'C') as 'Programming Language'

5. Using CHOOSE in a SELECT Statements
This time, we'll be using the AdventureWorks database and trying to see the employees' birth months. By the way, we'll be using two tables [HumanResources].[Employee] and [Person].[Person] for us to get the names of the employees and show the birth months.

Let's see the example below.
SELECT
    FORMATMESSAGE('%s, %s %s',
                    P.[LastName],
                    P.[FirstName],
                    ISNULL(P.[MiddleName], '')) AS  [FullName],
    E.[BirthDate],
    CHOOSE(MONTH(E.[BirthDate]),  'Jan.',
                                'Feb.',
                                'Mar.',
                                'Apr.',
                                'May.',
                                'Jun.',
                                'Jul.',
                                'Aug.',
                                'Sep',
                                'Oct.',
                                'Nov.',
                                'Dec.') as [Birth Month]
  FROM
  [AdventureWorks2019].[HumanResources].[Employee] E
  INNER JOIN [Person].[Person] P ON
  E.[BusinessEntityID] = P.[BusinessEntityID]

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