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Using PHPMYADMIN you can go to the table, Clik on Structure and the under ACTIONS edit the column that is giving you trouble. Then select NULL and save: Or if you prefer coding it directly on a query add the following: ALTER TABLE table_name CHANGE column_name column_name type DEFAULT NULL.
To add not null constraint to an existing column in MySQL, we will use the ALTER command. This is a type of validation to restrict the user from entering null values.
To enforce NOT NULL for a column in SQL Server, use the ALTER TABLE .. ALTER COLUMN command and restate the column definition, adding the NOT NULL attribute.
The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
This is possible with using a CHECK constraint:
CHECK (FirstIdentifier IS NOT NULL OR SecondIdentifier IS NOT NULL)
While CHECK constraints are part of the table (and hence "schema"?), they may not fit the desired definition. The above CHECK is not mutually exclusive, but it could be altered to such.
Happy coding.
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