CONCAT

CONCAT is a SQL function that allows you to concatenate, or join, two or more strings together. This is extremely useful whenever you need to combine text from multiple columns into a single column.

The syntax for the CONCAT function is quite simple:

CONCAT(string1, string2, ..., string_n)

This function accepts as input any number of string arguments, from two to as many as needed, and returns a new string which is the result of all the input strings joined together. The strings are concatenated in the order in which they are passed to the function.

Here's a simple example:

SELECT CONCAT('Hello', ' ', 'World');

This will return the string:

'Hello World'

You can also use CONCAT with columns from a table:

SELECT CONCAT(first_name, ' ', last_name) AS full_name
FROM employees;

The above query will return a new column full_name which is the result of first_name and last_name with a space in between. If first_name is 'John' and last_name is 'Doe', the returned full name would be 'John Doe'.

However, keep in mind that CONCAT will return NULL if any of the input strings is NULL. To avoid this, you can use the CONCAT_WS function which accepts a separator as the first argument and then a list of strings to concatenate.

SELECT CONCAT_WS(' ', first_name, last_name) AS full_name
FROM employees;

The CONCAT_WS function will ignore any NULL values, only joining the non-NULL values with the provided separator. Hence, 'John NULL' would become just 'John'.