Question

I am using a table “media_content” which has columns

id varchar(50) NOT NULL,
shorttitle varchar(200) DEFAULT NULL,
sourceimage blob

Later i modified the sourceimage column to default values as NULL

ALTER TABLE media_content
MODIFY COLUMN sourceimage VARCHAR(250) DEFAULT NULL;

Now i want to make the sourceimage column default as NONE, is it possible to do that?

Answer 1

You can specify the default value (of a string-type column) to be a string literal constant, such as 'NONE', but be aware that such a value has a very different meaning indeed to NULL (which indicates no value at all).

As documented under Working with NULL Values:

The NULL value can be surprising until you get used to it. Conceptually, NULL means “a missing unknown value” and it is treated somewhat differently from other values.

[ deletia ]

A common error when working with NULL is to assume that it is not possible to insert a zero or an empty string into a column defined as NOT NULL, but this is not the case. These are in fact values, whereas NULL means “not having a value.”

If you merely wish to present NULL values to your users in some other way, you should handle that at the presentation layer of your application.