How do you concatenate two strings in SQL?

To concatenate two strings in SQL, the approach slightly varies depending on the database system, but the concept remains the same — combining two or more strings into a single result.

In most SQL databases like SQL Server, I use the + operator. For example:

SELECT FirstName + ' ' + LastName AS FullName
FROM Employees;

This merges the first and last names with a space in between. It’s a clean and readable way to build full names, addresses, or custom labels.

In other databases like MySQL or PostgreSQL, the preferred way is to use the CONCAT() function:

SELECT CONCAT(FirstName, ' ', LastName) AS FullName
FROM Employees;

This method is safer because it automatically handles NULL values — in SQL Server, if either string is NULL, the entire result becomes NULL, whereas CONCAT() treats NULL as an empty string.

For example:

• In SQL Server: 'Aswini' + NULL → NULL
• In MySQL: CONCAT('Aswini', NULL) → 'Aswini'

In one project, I used string concatenation to dynamically generate email IDs for employees based on their names and company domain:

SELECT CONCAT(LOWER(FirstName), '.', LOWER(LastName), '@company.com') AS EmailID
FROM Employees;

This was particularly useful during onboarding automation to pre-fill default email fields.

A challenge I’ve faced was dealing with NULL values, which would break concatenation in SQL Server. To handle that, I used the ISNULL() or COALESCE() function to replace NULL with an empty string, like:

SELECT ISNULL(FirstName, '') + ' ' + ISNULL(LastName, '') AS FullName
FROM Employees;

In summary, string concatenation in SQL is straightforward but slightly syntax-dependent:

• + → SQL Server
• || → Oracle, PostgreSQL
• CONCAT() → MySQL, PostgreSQL (portable and safer)

I prefer CONCAT() for better null handling and cross-database compatibility.