Can the primary key of mysql be empty

The MySQL primary key must not be empty, otherwise it will damage the uniqueness of the database, reduce index efficiency, and even lead to unexpected errors. Primary keys must remain unique and non-null, which ensures data integrity and consistency and avoids greater problems in future development.

Can the MySQL primary key be empty? The answer is no, absolutely not. This is not a simple saying "No", there are so many tricks inside. Many beginners will make this mistake. At the least, it will lead to data redundancy, and at the worst, the entire database design will have to be overturned.

Let’s start with the basics. The primary key is the most awesome existence in the database, which ensures the uniqueness of each row of data in the table. Imagine, if the primary key is allowed to be empty, how can the database ensure uniqueness? What can it use to distinguish different rows? It’s like giving your house no license plate, and the same is true for your neighbor’s home. How can the postman deliver the express delivery? I can't give it to you at all!

To go a little further, the MySQL engine will do a lot of internal optimizations when processing primary keys. For example, the InnoDB engine uses B-tree index to manage primary keys, which is a very efficient index structure. But if you allow the primary key to be empty, the B-tree will not work properly, the index efficiency will be greatly reduced, and the query speed will be so slow that you doubt your life. What's worse is that all kinds of unexpected bugs may appear, which will make you scratch your head and eventually have to refactor the database.

Let’s take a look at the code. Although this article does not teach you how to write SQL, it is more intuitive to use code to explain it:

 <code class="sql">-- 创建一个表，主键是id，不允许为空CREATE TABLE users ( id INT PRIMARY KEY NOT NULL, username VARCHAR(255) ); -- 尝试插入一条主键为空的数据，你会发现会报错INSERT INTO users (username) VALUES ('John Doe');</code>

This code is simple, but it perfectly interprets the innocence of the primary key. NOT NULL constraints ensure this. If you miss NOT NULL , MySQL may allow you to insert null values, but this will pose huge hidden dangers.

Some people may say, then wouldn't it be enough if I use UUID or self-increment sequence as the primary key? Yes, this is a common method, but the key is that you have to make sure your primary key is unique and not empty . Although UUID can guarantee uniqueness, it is relatively long, takes up a lot of space, and may also be slightly less query efficiency. Self-increasing sequences is relatively efficient, but you should pay attention to concurrency problems and the problem of sequence exhaustion. Which primary key strategy to choose depends on your specific application scenario.

Speaking of this, you may already understand the harm of empty primary keys. It not only affects the performance and efficiency of the database, but more importantly, it destroys the integrity and consistency of the database design. So, remember this iron rule: MySQL primary key must not be empty! This is not only a grammatical rule, but also a basic principle of database design. Don’t leave hidden dangers to save trouble, which will make you pay a greater price in future development. Trust me, this is definitely a bloody lesson summary of experience.

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