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Character set and sorting rules issues are common when cross-platform migration or multi-person development, resulting in garbled code or inconsistent query. There are three core solutions: First, check and unify the character set of database, table, and fields to utf8mb4, view through SHOW CREATE DATABASE/TABLE, and modify it with ALTER statement; second, specify the utf8mb4 character set when the client connects, and set it in connection parameters or execute SET NAMES; third, select the sorting rules reasonably, and recommend using utf8mb4_unicode_ci to ensure the accuracy of comparison and sorting, and specify or modify it through ALTER when building the library and table.
The problem of character sets and sorting rules in MySQL is actually quite common. Especially when you migrate data across platforms or multiple developers using different environments, it is easy to have garbled code or inconsistent query results. The core problem is that the character set is not unified, or the collation is not set properly.

The following scenarios basically cover the pain points that most people will encounter.

Check and unify the character set of databases, tables, and fields
Many people start to build libraries and tables after installing MySQL, ignoring the problem of default character sets. For example, the default version of MySQL is latin1. If you store Chinese, there must be a problem.
It is recommended that you use utf8mb4 from libraries to tables to fields, which is the best choice for supporting emoji and most languages.

You can check this way:
-
View the database default character set:
SHOW CREATE DATABASE your_db;
View the character set of a table:
SHOW CREATE TABLE your_table;
Modify the database character set:
ALTER DATABASE your_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
Modify the table character set:
ALTER TABLE your_table CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
These operations do not have to be completed at one time, but the earlier the unified, the better, to avoid the subsequent data being mixed and difficult to process.
The character set must also be specified when connecting to the client
Sometimes your database itself is fine, but after connecting through the program, it will be garbled as soon as it is stored in Chinese. At this time, it is likely that the character set is not set correctly when the client connects.
For example, if you execute SET NAMES 'utf8'
in your application, but you should actually use utf8mb4
, which will also cause problems. Especially when connecting to MySQL in Java and PHP, pay special attention to the configuration in the connection string.
A common practice is to execute it immediately after the connection:
SET NAMES 'utf8mb4';
Or add:
charset=utf8mb4
Different languages ??have different writing methods. For example, PDO can be written in PHP like this:
new PDO('mysql:host=localhost;dbname=test;charset=utf8mb4', 'user', 'pass');
Don’t underestimate this step. Many cases where “the database is fine, the code is faulty” are all missed here.
Only when the sorting rules are selected correctly will the search be accurate
The character set is done, and the sorting rules cannot be messed up. Collation determines how characters are compared and sorted, such as whether the case is sensitive, how to sort in Chinese, etc.
Common ones are utf8mb4_unicode_ci
and utf8mb4_general_ci
, which means case-insensitive (case-insensitive). It is generally recommended to use _unicode_ci
, which is more in line with language habits, although the performance is slightly worse.
For example:
If you use utf8mb4_general_ci
, you may take some special characters as the same; utf8mb4_unicode_ci
will more accurately identify their differences.
The modification method is also very simple. When building a library or table, add:
COLLATE utf8mb4_unicode_ci
If it already exists, you can also use the ALTER statement to modify it like before.
Basically that's it. It’s not too difficult to say it’s difficult, but if you really don’t pay attention to it in the early stage, it’s really a headache to investigate it later. Therefore, it is the most convenient way to be able to unify the character set and sorting rules from the beginning.
The above is the detailed content of Handling character sets and collations issues in MySQL. For more information, please follow other related articles on the PHP Chinese website!

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