Database data insertion, NULL and non-null judgments, automatic sorting, constrained primary keys, unique constraints, external health constraints

1. View table structure

2. Inserting data

3. Null and non-null judgments

For example, adding data defaults to NULL, and if we don't want to be empty, then

, the username is set to NOT NULL, the data is inserted if the data is null when the error, such as: Age can be null, insert Zfyan when the age is null, no error

4. Automatic sorting auto_increment

Must have a primary key

5. Primary KEY constraint, UNIQUE constraint

A PRIMARY KEY constraint is unique, and a unique constraint can be multiple

Database data insertion, NULL and non-null judgments, automatic sorting, constrained primary keys, unique constraints, external health constraints