Is mysql query case sensitive?

MySQL's case sensitivity depends on the character set and proofreading rules: _ci proofreading rules are case-insensitive and are suitable for most application scenarios, but may pose security risks. _bin proofreading rules are case sensitive and are used for precise matching and data integrity, but can lead to query complexity. Character sets define the way characters are stored, while proofreading rules stipulate the way characters are compared. Character sets and proofreading rules can be set at both the database and table levels. Inconsistent encoding, ignoring case security risks and performance differences are common problems.

MySQL query is case sensitive? There is only one truth!

This question seems simple, but it actually has a secret. The answer is: It depends on the situation . Do you think I'm perfunctory? No, this is the key to understanding MySQL case sensitivity. It is not as simple and crude as some languages, but rather depends on a clever combination of factors. After reading this article, you will no longer be troubled by this problem and will even gain insight into some of the mysteries of the underlying MySQL.

Basic knowledge laying the foundation: character sets and proofreading rules

MySQL's case sensitivity fundamentally depends on the character set and proofreading rules you choose. Character sets define how the database stores characters, while proofreading rules stipulate how characters are compared. They are like twin brothers, neither of them is missing. For example, utf8mb4 is a commonly used character set, but it does not determine case sensitivity by itself. The real decision lies in the proofreading rules you specify for that character set.

Let me give you a chestnut: utf8mb4_general_ci and utf8mb4_bin are two different proofreading rules. _ci usually means case-insensitive insensitive, while _bin means case-sensitive sensitive, which performs binary comparisons.

Core concept: In-depth understanding of the impact of proofreading rules

_ci proofreading rules ignore case differences when comparing characters, which is very convenient in many cases and meet the needs of most application scenarios. But it also means you can't distinguish subtle differences in case. Imagine if your username allows case mixing, admin and Admin become the same user, which may pose a security risk.

The _bin proofreading rules are completely different, and they compare characters bit by bit, so case differences will be strictly distinguished. This means that admin and Admin will be treated as completely different strings. This is useful in situations where exact matches are required, such as password storage or data integrity verification. However, it also increases the complexity of the query and can lead to some unnecessary troubles, such as forgetting case and causing the query to fail.

Practical drill: Code examples and analysis

Suppose we have a table called users , containing a username column, whose character set and proofreading rules are utf8mb4_general_ci and utf8mb4_bin , respectively.

Proofreading rules using utf8mb4_general_ci :

 <code class="sql">CREATE TABLE users ( id INT PRIMARY KEY AUTO_INCREMENT, username VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci ); INSERT INTO users (username) VALUES ('admin'), ('Admin'); SELECT * FROM users WHERE username = 'admin'; -- 这条语句会返回两行记录SELECT * FROM users WHERE username = 'Admin'; -- 这条语句也会返回两行记录</code>

Proofreading rules using utf8mb4_bin :

 <code class="sql">CREATE TABLE users_bin ( id INT PRIMARY KEY AUTO_INCREMENT, username VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin ); INSERT INTO users_bin (username) VALUES ('admin'), ('Admin'); SELECT * FROM users_bin WHERE username = 'admin'; -- 这条语句只返回一行记录('admin') SELECT * FROM users_bin WHERE username = 'Admin'; -- 这条语句只返回一行记录('Admin')</code>

Advanced usage: Database level and table level settings

You can set character sets and proofreading rules at the database level and table level respectively. Database level settings affect all newly created tables under that database unless you explicitly specify other proofreading rules when creating the table. This requires careful consideration, because once set up, it is more troublesome to modify.

FAQs and Solutions: A Guide to Troubleshooting

• Inconsistent encoding: If your application code and the database character set are inconsistent, it may cause garbled code or uppercase and case problems. It is crucial to ensure that they are consistent.
• Ignore the security risks caused by uppercase and lowercase cases: Using _ci proofreading rules on sensitive information such as usernames or passwords may bring security risks. It is recommended to use _bin or other safer solutions.
• Performance Difference: _bin proofreading rules may be slightly slower than _ci , but in most cases, this difference is negligible.

Performance Optimization and Best Practice: Experience Talk

Choosing the right character set and proofreading rules is critical, it directly affects your database performance and security. When designing a database, carefully weigh the advantages and disadvantages of _ci and _bin and choose the solution that best suits your application scenario. Try to avoid unnecessary type conversion in query conditions, which will reduce query efficiency. Developing good database design habits is more important than any optimization technique.

In short, MySQL's case sensitivity is not a simple "yes" or "no" question, but a complex topic that requires you to have a deep understanding of character sets and proofreading rules. I hope this article can help you fully master this knowledge point and go further on the road of database development.

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