How to express non-null in mysql

There are two ways to express non-null in MySQL: using NOT NULL constraints to prohibit fields from being null. Use the DEFAULT value to specify a default value for fields that are not explicitly specified.

How to express non-null in MySQL

In MySQL, non-null is usually expressed as NULL values ​​are not allowed. There are two main ways to represent non-null:

1. NOT NULL constraint

• Use NOT NULL constraint mandatory fields are not allowed NULL value.
• For example: CREATE TABLE my_table (id INT NOT NULL);

2. DEFAULT value

• Use the DEFAULT value to specify a default value for the field, even if the value is not explicitly specified.
• For example: CREATE TABLE my_table (name VARCHAR(255) DEFAULT 'John Doe');

Detailed description:

• NOT NULL constraint:

  • Ensure that a field can never store NULL values.
  • If you try to insert or update a NULL value, an error will be triggered.

• DEFAULT value:

  • Provides a default value for fields that are not explicitly specified when inserting or updating records .
  • DEFAULT value can be any valid value, including number, string, or date.
  • Even if NULL values ​​are allowed, using a DEFAULT value prevents field values ​​from being empty.

Note:

• By default, most MySQL data types (such as INT and VARCHAR) allow NULL values.
• If a field needs to be non-null, you must explicitly use the NOT NULL constraint or DEFAULT value.
• For fields that require mandatory non-null values ​​(such as primary keys or foreign keys), it is recommended to use NOT NULL constraints.
• For fields that require a default value (such as name or address), it is recommended to use the DEFAULT value.

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