I can't use input in Mysql procedure - mysql

Question

I how defined a procedure in MySql which has an input and input will be a name of column that will be added to table 'test1' but sql names that column input instead of using the value of input .how can i do this in the right way?
DELIMITER
CREATE PROCEDURE p1
(IN input CHAR(20))
BEGIN
ALTER TABLE test1
ADD COLUMN input char(20);
END
DELIMITER ;

Answer 1

You should google dynamic sql and read the manual https://dev.mysql.com/doc/refman/8.0/en/sql-syntax-prepared-statements.html
In the meantime here's an example.
drop procedure if exists p;
alter table users
drop column abc;
DELIMITER $$
CREATE PROCEDURE p
(IN input CHAR(20))
BEGIN
#ALTER TABLE test1
#ADD COLUMN input char(20);
set #sql = concat('alter table users add column ',input,' char(20);');
select #sql;
prepare sqlstmt from #sql;
execute sqlstmt;
deallocate prepare sqlstmt;
END $$
DELIMITER ;
call p('abc');
describe users;
MariaDB [sandbox]> call p('abc');
+--------------------------------------------+
| #sql |
+--------------------------------------------+
| alter table users add column abc char(20); |
+--------------------------------------------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.42 sec)
MariaDB [sandbox]> describe users;
+---------------------+-------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+-------------+------+-----+-------------------+-------+
| id | int(11) | NO | PRI | NULL | |
| userName | varchar(60) | NO | | NULL | |
| photo | varchar(50) | YES | | NULL | |
| status | int(11) | YES | | NULL | |
| ts | datetime | YES | | CURRENT_TIMESTAMP | |
| events_participated | int(11) | YES | | NULL | |
| fb_uid | int(11) | YES | | NULL | |
| Column_name | varchar(10) | YES | | NULL | |
| post_type | varchar(10) | YES | | NULL | |
| password | varchar(8) | YES | | NULL | |
| abc | char(20) | YES | | NULL | |
+---------------------+-------------+------+-----+-------------------+-------+
11 rows in set (0.03 sec)