The mysql primary key can be varchar

The MySQL primary key can be used with VARCHAR, but it is strongly recommended not to use it. VARCHAR is a variable-length string type that will reduce engine efficiency, poor index optimization, and take up more storage space. The primary key of the INT type is a fixed-length integer type. The B-tree index utilization rate is high, the search speed is fast, and the space is less. Unless there is a special need, it is recommended to use INT, BIGINT or self-growing sequences as primary keys.

Can MySQL primary key use VARCHAR? Listen to the heartfelt words of those who have experienced it

Many newbies, even some veterans, are a little confused about using VARCHAR for MySQL primary keys. The answer is: Yes, but strongly not recommended! This article is about why. After reading it, you can not only understand why it is not recommended to use VARCHAR as the primary key, but also have a deeper understanding of database design and avoid falling into those headache-prone pits.

Let’s start with the basics. The primary key, as the name suggests, is a unique identifier in the database table, used to quickly locate records. VARCHAR is a variable-length string type. On the surface, it seems that there is no problem with using VARCHAR as the primary key, after all, it can guarantee uniqueness.

But the problem lies in the four words "variable length". The MySQL engine's efficiency is greatly reduced when processing VARCHAR primary keys. Why? Because the engine takes extra time to calculate the string length, compare and sort. Think about it, if your table has millions or even tens of millions of records, and each query requires a large number of string comparisons, how much performance overhead is this? It's like running the F1 track with a tractor, you know.

Worse, the InnoDB engine (which is used in most cases) does not perform well on the index optimization of VARCHAR primary keys. It uses the B-tree index, and the node size of the B-tree is fixed. The VARCHAR length is not fixed, resulting in low utilization of B-tree nodes, increasing disk IO operations, which in turn affects query speed. This is like using a box of different sizes to hold things, with extremely low space utilization and naturally low efficiency.

So why are primary keys of INT type efficient? Because INT is a fixed-length integer type, the B-tree node has high utilization rate and fast search speed. Just like using a standard-sized box to hold things, the space utilization rate is high and the efficiency is naturally high.

Let’s talk about the pitfalls in practical applications. Suppose you use UUID (a common VARCHAR primary key generation method) as the primary key, and its length is usually 36 characters. Just imagine, each record needs to store 36 characters, which takes up much larger space than the INT type. If your table is large, the space overhead is also considerable.

Of course, it does not mean that VARCHAR must not be used as the primary key. In some special scenarios, such as the need to ensure the readability of the primary key, or the primary key itself is a string type, you can consider using VARCHAR. But this is very rare and requires careful weighing of the pros and cons.

Below, let’s take a look at the code and experience the performance differences between INT primary key and VARCHAR primary key:

 <code class="sql">-- 创建INT主键表CREATE TABLE int_primary_key ( id INT PRIMARY KEY, name VARCHAR(255) ); -- 创建VARCHAR主键表CREATE TABLE varchar_primary_key ( id VARCHAR(36) PRIMARY KEY, name VARCHAR(255) ); -- 插入大量数据(这里省略了插入数据的代码，你可以自己动手试试) -- 查询性能测试(这里也省略了性能测试代码，建议用工具进行测试，例如MySQL自带的性能测试工具)</code>

Run the test yourself and you will find that the query speed of the INT primary key is significantly faster than the VARCHAR primary key.

Finally, my advice is: Never use VARCHAR as the primary key unless there are very special needs. Only by selecting INT, BIGINT or self-growing sequences as primary keys can the performance and efficiency of the database be ensured. Remember that database design is a system project, and choosing the right data type is crucial to the overall performance of the system. Don’t lay hidden dangers for the sake of temporary convenience. Remember the experience!

The above is the detailed content of The mysql primary key can be varchar. For more information, please follow other related articles on the PHP Chinese website!