MySQL排序规则冲突错误:Illegal mix of collations的问题解决

SQL 错误 [1267] [HY000]: Illegal mix of collations (utf8mb4_0900_ai_ci,IMPLICIT) and (utf8mb4_general_ci,IMPLICIT) for operation '='

SELECT *
FROM orders o
JOIN users u ON o.user_id = u.id  -- 冲突点：两个表的排序规则不同

SET @var = 'test';
SELECT * FROM products WHERE name = @var;  -- 变量默认使用 utf8mb4_general_ci

SELECT *
FROM orders
WHERE user_id IN (
  SELECT id FROM users WHERE status = 'active'  -- 子查询结果排序规则不同
);

SELECT * FROM products WHERE id = '123abc';  -- 字符串与数字的隐式转换导致排序规则冲突

-- 修改列排序规则
ALTER TABLE users
MODIFY COLUMN id INT(11) NOT NULL AUTO_INCREMENT COLLATE utf8mb4_0900_ai_ci;

-- 修改表默认排序规则
ALTER TABLE orders
CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

-- 方法1：列级别指定
SELECT *
FROM orders o
JOIN users u ON o.user_id COLLATE utf8mb4_0900_ai_ci = u.id COLLATE utf8mb4_0900_ai_ci;

-- 方法2：会话级设置
SET NAMES 'utf8mb4' COLLATE 'utf8mb4_0900_ai_ci';

-- 修改数据库默认排序规则
ALTER DATABASE my_database
CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

-- 处理变量冲突
SET @var = 'test' COLLATE utf8mb4_0900_ai_ci;

-- 处理临时表
CREATE TEMPORARY TABLE temp_users (
  id INT(11) NOT NULL,
  name VARCHAR(50) COLLATE utf8mb4_0900_ai_ci
);

-- 查看数据库默认规则
SELECT DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME
FROM INFORMATION_SCHEMA.SCHEMATA
WHERE SCHEMA_NAME = 'my_database';

-- 查看表结构
SHOW CREATE TABLE orders;