How do you use CONCAT_WS function in T-SQL

Title: Mastering String Concatenation in T-SQL with CONCAT_WS Function

In the realm of database management systems, particularly in Microsoft SQL Server, working with strings is an essential skill. One of the most commonly used string manipulation functions is CONCAT_WS (Concatenate With Delimiter). This function is used to concatenate (join) multiple strings with a specified delimiter. In this blog post, we will delve deep into understanding the usage, syntax, and practical applications of the CONCAT_WS function in T-SQL.

**Understanding Strings and Concatenation**

Before we dive into the specifics of the CONCAT_WS function, let's first discuss strings and concatenation in T-SQL. In SQL Server, strings are enclosed within single quotes ('). For instance, 'Hello World' is a string literal.

Concatenation is the process of joining two or more strings together to form a new string. In T-SQL, we can concatenate strings using the + operator or the CONCAT() function.

sql
-- Using + operator
SELECT 'Hello' + ' ' + 'World' AS ConcatenatedString;
-- Using CONCAT() function
SELECT CONCAT('Hello', ' ', 'World') AS ConcatenatedString;

Both of these methods yield the same result: 'Hello World'.

**Introducing CONCAT_WS Function**

The CONCAT_WS function is an alternative way of concatenating strings with a delimiter in SQL Server. It stands for "Concatenate With Spaces" because it adds a space by default between each string being concatenated.

The syntax for using the CONCAT_WS function is as follows:

sql
CONCAT_WS(delimiter, string1, string2, ...)

Here, 'delimiter' is the string that separates each concatenated string, and 'string1', 'string2', etc., are the strings that need to be concatenated.

**Example Usage of CONCAT_WS Function**

Let's consider an example where we have a table named 'Employees' with columns 'FirstName' and 'LastName'. We want to create a new column 'FullName' that concatenates 'FirstName' and 'LastName' with a space as a delimiter.

sql
CREATE TABLE Employees (
    ID INT PRIMARY KEY IDENTITY(1,1),
    FirstName VARCHAR(50),
    LastName VARCHAR(50)
);
INSERT INTO Employees (FirstName, LastName) VALUES ('John', 'Doe'), ('Jane', 'Doe'), ('Mike', 'Smith');
-- Using CONCAT_WS function
ALTER TABLE Employees ADD FullName AS (CONCAT_WS(' ', FirstName, LastName));
SELECT * FROM Employees;

Output:

| ID | FirstName | LastName | FullName |

| --- | --- | --- | --- |

| 1 | John | Doe | John Doe |

| 2 | Jane | Doe | Jane Doe |

| 3 | Mike | Smith | Mike Smith |

**Using Different Delimiters**

The CONCAT_WS function is not limited to spaces as delimiters; we can use any string as a delimiter. For instance, let's create a new column 'EmailID' that concatenates 'FirstName' and 'LastName' with '@example.com' as a delimiter.

sql
ALTER TABLE Employees ADD EmailID AS (CONCAT_WS('@example.com', FirstName, LastName));
SELECT * FROM Employees;

Output:

| ID | FirstName | LastName | FullName | EmailID |

| --- | --- | --- | --- | --- |

| 1 | John | Doe | John Doe | [email protected] |

| 2 | Jane | Doe | Jane Doe | [email protected] |

| 3 | Mike | Smith | Mike Smith | [email protected] |

**Performance Comparison**

It's essential to understand that while both + operator and CONCAT_WS function achieve the same goal