CONCAT_WS (Transact-SQL)
Applies to: 
SQL Server 2017 (14.x) and later
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
This function returns a string resulting from the concatenation, or joining, of two or more string values in an end-to-end manner. It separates those concatenated string values with the delimiter specified in the first function argument. (CONCAT_WS indicates concatenate with separator.)
Syntax
CONCAT_WS ( separator , argument1 , argument2 [ , argumentN ] ... )
Arguments
separator
An expression of any character type (char, nchar, nvarchar, or varchar).
argument1, argument2 [ , argumentN ]
An expression of any string value. The CONCAT_WS function requires at least two arguments, and no more than 254 arguments.
Return types
A string value whose length and type depend on the input.
Remarks
CONCAT_WS takes a variable number of string arguments and concatenates (or joins) them into a single string. It separates those concatenated string values with the delimiter specified in the first function argument. CONCAT_WS requires a separator argument and a minimum of two other string value arguments; otherwise, CONCAT_WS raises an error. CONCAT_WS implicitly converts all arguments to string types before concatenation.
The implicit conversion to strings follows the existing rules for data type conversions. For more information about behavior and data type conversions, see CONCAT (Transact-SQL).
Treatment of NULL values
CONCAT_WS ignores the SET CONCAT_NULL_YIELDS_NULL { ON | OFF } setting.
If CONCAT_WS receives arguments with all NULL values, it returns an empty string of type varchar(1).
CONCAT_WS ignores null values during concatenation, and doesn't add the separator between null values. Therefore, CONCAT_WS can cleanly handle concatenation of strings that might have "blank" values - for example, a second address field. For more information, see Example B.
If a scenario involves null values separated by a delimiter, consider the ISNULL function. For more information, see Example C.
Examples
A. Concatenate values with separator
This example concatenates three columns from the sys.databases table, separating the values with a hyphen surrounded by spaces (-).
SELECT CONCAT_WS(' - ', database_id, recovery_model_desc, containment_desc) AS DatabaseInfo
FROM sys.databases;
Here's the result set.
DatabaseInfo
-----------------
1 - SIMPLE - NONE
2 - SIMPLE - NONE
3 - FULL - NONE
4 - SIMPLE - NONE
B. Skip NULL values
This example ignores NULL values in the arguments list, and uses a comma separator value (,).
SELECT CONCAT_WS(',', '1 Microsoft Way', NULL, NULL, 'Redmond', 'WA', 98052) AS Address;
Here's the result set.
Address
--------------------------------
1 Microsoft Way,Redmond,WA,98052
C. Generate CSV-formatted data from table
This example uses a comma separator value (,), and adds the carriage return character CHAR(13) in the column separated values format of the result set.
SELECT STRING_AGG(CONCAT_WS(',', database_id, recovery_model_desc, containment_desc), CHAR(13)) AS DatabaseInfo
FROM sys.databases;
Here's the result set.
DatabaseInfo
-------------
1,SIMPLE,NONE
2,SIMPLE,NONE
3,FULL,NONE
4,SIMPLE,NONE
CONCAT_WS ignores NULL values in the columns. Wrap a nullable column with the ISNULL function, and provide a default value. For example:
SELECT STRING_AGG(
CONCAT_WS(',', database_id, ISNULL(recovery_model_desc, ''),
ISNULL(containment_desc, 'N/A')
), CHAR(13)) AS DatabaseInfo
FROM sys.databases;