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MySQL Not Null

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MySQL NOT NULL Constraint

The NOT NULL constraint in MySQL ensures that a column cannot store NULL values. It is used when you want to ensure that a column always contains a value and cannot be left empty.



NOT NULL on CREATE TABLE


Syntax:

CREATE TABLE table_name (
  column1 data_type NOT NULL,
  column2 data_type,
  column3 data_type NOT NULL
);


Example

Example
CREATE TABLE students (
student_id INT PRIMARY KEY,
name VARCHAR(50) NOT NULL,
email VARCHAR(100),
age INT NOT NULL
);

Explanation:

  • name and age cannot be NULL.
  • email can accept NULL values.


NOT NULL on ALTER TABLE



Syntax:


ALTER TABLE table_name
MODIFY column_name data_type NOT NULL;


Example:

Example
ALTER TABLE students
MODIFY email VARCHAR(100) NOT NULL;

Explanation:

  • This makes the email column mandatory, ensuring it cannot store NULL values.



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