How to make sure that the column value is always added in Uppercase? - mysql

Question

I have an existing column host and want to make sure that the column value host is always added in Uppercase.
I am using Alter Table command as below:
ALTER TABLE `mydb`.`myTable`
CHANGE COLUMN `host` `host`
VARCHAR(255) GENERATED ALWAYS AS (UPPER()) STORED;
This is causing an error and I am not able to alter the column.
Operation failed: There was an error while applying the SQL script to the database.
ERROR 1582: Incorrect parameter count in the call to native function 'UPPER'
SQL Statement:
ALTER TABLE mydb.myTable
CHANGE COLUMN host host VARCHAR(255) GENERATED ALWAYS AS (UPPER()) VIRTUAL
I want to make sure that moving forward the value inserted in host is always in uppercase.
I want to achieve this by updating the value in uppercase at runtime.
I don't want to add any constraint as it will cause an error when the host value is entered in lowercase.

Answer 1

It is not entirely clear what you are trying to do.
If you want to set a constraint on the table that allows only upper case letters in host, use a check constraint:
alter table mytable
add constraint chk_host_upper
check (host rlike '^[A-Z]*$')
;
This prevents lower case character to be written to the column; an attempt to do so results in a runtime error.
If, on the other hand, you want to create a new column, that returns the upper case value of host, regardless of the actual column code:
alter table mytable
add column host_upper varchar(50) -- same as the original column
as (upper(host))
;
With this set up at hand, you can query the new column host_upper when you want the upper case values.
Finally: if you want to convert input value to upper case on the fly on inserts, then you need a trigger:
delimiter //
create trigger mytrigger
before insert on mytable
for each row
begin
set new.host = upper(new.host);
end
//
delimiter ;

Answer 2

You can just assign the host column to have a case insensitive collation:
ALTER TABLE mydb.myTable MODIFY host VARCHAR(255)
CHARACTER SET latin1
COLLATE latin1_swedish_ci;
Now the case of the host you use when inserting does not matter, and you may compare against this column using any case. If you still need to view the host as uppercase, then just use UPPER():
SELECT UPPER(host) AS host_upper
FROM myTable;