MySQL Manual | 13.3 String Functions

MySQL Manual | 13.3 String Functions: "CONCAT(str1,str2,...)
Returns the string that results from concatenating the arguments. Returns NULL if any argument is NULL. May have one or more arguments. A numeric argument is converted to its equivalent string form.

mysql> SELECT CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> SELECT CONCAT('My', NULL, 'QL');
-> NULL
mysql> SELECT CONCAT(14.3);
-> '14.3'"