Скачать или смотреть Joining strings by using CONCAT and handling NULL value.

https://www.plus2net.com/sql_tutorial...

We can join strings by using CONCAT function.
SELECT CONCAT(‘string1’,’-‘,’string2’)
Output
String1-string2
WE will apply this to our sample table which is having f_name and l_name columns.
SELECT f_name,l_name,
CONCAT(f_name,' ',l_name) as name,class FROM `student_name`

WE can observe when ever NULL data is present the output is NULL.
SELECT CONCAT(Null, ‘-‘,’String2’)
Output
NULL


To handle such NULL data we can use COALESCE
SELECT f_name,l_name,
CONCAT(COALESCE(f_name,'-',' '),' ',COALESCE(l_name,'-')) as name,
class FROM `student_name`

We can join three columns by using CONCAT
SELECT CONCAT ( f_name,'/',l_name,'/',class) as file_name
FROM `student_name`