Defining Effective Primary Keys in MySQL Tables
Jul 09, 2025 am 01:41 AM
The primary key is a field or combination that uniquely identifies records in a database table. Four principles must be followed when selecting: 1. Priority is given to using self-incremental integers such as INT or BIGINT to improve efficiency; 2. Avoid long strings such as UUID or mailboxes to avoid affecting performance; 3. Use business fields with caution, such as ID number due to poor stability; 4. Try not to use composite primary keys to maintain due to their complexity. At the same time, pay attention to the self-value-added configuration, delete the ID and do not recycle it, and do not manually insert the self-added field.
In MySQL database design, choosing a suitable primary key is a key step in building an efficient and stable table structure. The primary key not only determines the uniqueness constraints of the data, but also directly affects the index performance and query efficiency.
What is a primary key?
A primary key is a field or combination of fields used in a table to uniquely identify each row of records. It must meet two basic conditions:
- Uniqueness : Each value must be unique throughout the table
- Non-empty : NULL values ??are not allowed
Usually we will specify a primary key for each table, and MySQL will automatically create a clustered index for it, which makes primary key-based query very efficient.
Principle of selecting primary keys
When choosing a primary key, you don’t just choose a field. There are several key points that need to be paid attention to:
Try to use simple, self-increasing integer types
For example, theAUTO_INCREMENTfield ofINTorBIGINTtype, this type of primary key insertion is efficient, has a small space, and is easy to maintain the index structure.Avoid using long strings as primary keys
For example, using email address, UUID, etc. as primary keys can ensure uniqueness, but it will cause the index size to grow, affecting the writing speed and query performance.Consider whether business logic requires natural primary keys
Sometimes we want to directly use meaningful fields in the business as the primary key, such as ID number, order number, etc. However, this type of "natural primary key" is often not stable enough and is costly to modify, so it is recommended to use it with caution.Use the compound primary key with caution
Although multiple fields can be combined into primary keys, it increases complexity in actual development, especially when associated queries and foreign key references are more prone to errors.
Comparison of common primary key types
| Primary Key Type | Recommended | illustrate |
|---|---|---|
| Self-increasing integer | ? Recommended | Fast insertion, high index efficiency |
| UUID | ? Not recommended | Slow query, large index occupies |
| Business fields (such as mobile phone number) | ?? Use with caution | May change, affecting foreign keys |
| Compound primary key | ?? If you can, don't use it | Trouble maintenance and poor scalability |
Things to note when using auto-increment primary key
If you choose to use AUTO_INCREMENT to generate primary keys, the following details are worth noting:
- The starting point and step size of the value-added value can be configured and is suitable for ID allocation strategies in certain database and table scenarios.
- Deleting a record will not recycle the ID , which means that even if you delete a record, its ID will not be reused.
- Don't insert self-value fields manually , unless you know what you are doing, it can easily cause conflict or confusion.
Basically that's it. The primary key looks simple, but whether you choose well or not has a great impact on the long-term operation of the database. Don’t bury the pit for the future.
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