How to add not null constraint to existing column in MySQL
Just use an ALTER TABLE... MODIFY...
query and add NOT NULL
into your existing column definition. For example:
ALTER TABLE Person MODIFY P_Id INT(11) NOT NULL;
A word of caution: you need to specify the full column definition again when using a MODIFY
query. If your column has, for example, a DEFAULT
value, or a column comment, you need to specify it in the MODIFY
statement along with the data type and the NOT NULL
, or it will be lost. The safest practice to guard against such mishaps is to copy the column definition from the output of a SHOW CREATE TABLE YourTable
query, modify it to include the NOT NULL
constraint, and paste it into your ALTER TABLE... MODIFY...
query.
Would like to add:
After update, such as
ALTER TABLE table_name modify column_name tinyint(4) NOT NULL;
If you get
ERROR 1138 (22004): Invalid use of NULL value
Make sure you update the table first to have values in the related column (so it's not null)
Try this, you will know the difference between change and modify,
ALTER TABLE table_name CHANGE curr_column_name new_column_name new_column_datatype [constraints]
ALTER TABLE table_name MODIFY column_name new_column_datatype [constraints]
- You can change name and datatype of the particular column using
CHANGE
. - You can modify the particular column datatype using
MODIFY
. You cannot change the name of the column using this statement.
Hope, I explained well in detail.