Drop default constraint - mysql

Question

I have a tableA with following output from desc tableA command:
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | | | |
| city | varchar(50) | YES | | NULL | |
| state | char(2) | YES | | NULL | |
| country | varchar(30) | YES | | NULL | |
| notes | longtext | YES | | NULL | |
| type | varchar(50) | NO | | NULL | |
+---------+-------------+------+-----+---------+----------------+
Now there are 3 columns with NOT NULL constraints:
id
name
type
For columns id and type, I need to remove the default constraint. Basically I want Default: None. I do not want to use the workarounds eg . setting default to '' for a varchar.
The difference between NULL, NONE, and '' is made more clear from this discussion Default-values-for-varchar-and-int-mysql-data-types
I tried using the command:
alter table tableA alter column type drop default;
The query runs fine, but no rows are affected. And no change in Default value is shown when I run describe command.
If I set the default value to '' I run into different issue - the database allows the entry of empty string in the db. For me that is equivalent to inserting NULL for a column's value, and I do not want to allow that.
I need some guidance on how to handle Default values in this situation where I cannot allow empty strings as data in the db. I want to mention that I am planning to put validations in the code to check if the incoming data is an empty string or NULL. But just in case that validation is not working etc, I want to make sure the DB can refuse to add such data.
Any help is really appreciated.

Answer 1

If the column can be then null, then either default or null are the same.
So Allowed Null, Default null is effectively irrelevant except when doing say
Insert (name,city,type) Values ('Fred',DEFAULT,'Caucasian')
Null isn't an empty string. Given you are allowing null in the table but interpreting it as empty string in your application, you have an irritating flaw in your design.
If you don't want empty strings in there, normally you'd use a check constraint which as far as I know still isn't implemented in mysql. Apparently this lack is usually solved with an insert trigger.
So you'd check the value in the trigger and then fail the insert for empty strings.
PS it doesn't solve the integrity problem, but if you did want a way to put nulls in when a straing was empty so you would not have to distinguish between empty string and null.
Then have a look at the nullif function.