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How does MySQL choose the correct character set?

MySQL uses character sets and collations to manage how text data is stored, compared, and sorted in the database. A character set is a collection of characters with corresponding encoding, and a collation defines the rules for comparing characters within a character set.

When MySQL chooses a character set for storing or manipulating text data, it follows a hierarchy of settings to determine the correct one. Here is the hierarchy, from the highest to the lowest priority:

Column level: If a character set is explicitly specified when defining a column in a table, MySQL uses that character set for the column.
Example:
```
CREATE TABLE example (
    text_column VARCHAR(255) CHARACTER SET utf8mb4
);
```
Table level: If a character set is not specified at the column level, MySQL looks for a character set defined at the table level. If one is specified, it will be used for all columns in the table that do not have an explicitly defined character set.
Example:
```
CREATE TABLE example (
    text_column VARCHAR(255)
) CHARACTER SET utf8mb4;
```
Database level: If a character set is not specified at the column or table level, MySQL looks for a character set defined at the database level. If one is specified, it will be used for all tables and columns within the database that do not have an explicitly defined character set.
Example:
```
CREATE DATABASE example_db
CHARACTER SET utf8mb4;
```
Server level: If a character set is not specified at the column, table, or database level, MySQL uses the default character set defined at the server level. You can check the server-level character set and collation by running the following commands:
```
SHOW VARIABLES LIKE 'character_set_server';
SHOW VARIABLES LIKE 'collation_server';
```
If you want to change the default character set and collation at the server level, you can edit your MySQL server configuration file (e.g., my.cnf or my.ini) and add or modify the following lines:
```
[mysqld]
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
```
After making changes, restart your MySQL server for the new settings to take effect.

By understanding the hierarchy of character set settings in MySQL, you can ensure that your text data is stored and processed correctly, and that the appropriate character set and collation are used for your specific requirements.

Specifying character set in MySQL queries:
- Developers can explicitly set character sets in MySQL queries using the CHARACTER SET clause, ensuring consistency in data handling.
```
SELECT * FROM table_name WHERE column_name = 'value' COLLATE utf8mb4_general_ci;
```
Changing character set at runtime in MySQL:
- Character sets can be adjusted at runtime for specific connections using the SET NAMES statement.
```
SET NAMES 'utf8mb4';
```