mysql如何将一个列按逗号分割为多列

CREATE TABLE my_table (
    id INT AUTO_INCREMENT PRIMARY KEY,
    date DATE,
    tags VARCHAR(255)
);

INSERT INTO my_table (date, tags) VALUES
('2024-06-01', 'tag1'),
('2024-06-11', 'tag1,tag2'),
('2024-06-21', 'tag1,tag2,tag3');

-- 统计每个标签的出现次数
SELECT 
    split_tags.tag, 
    COUNT(*) AS count
FROM 
-- 创建临时表存储拆分的标签
(
  SELECT 
      id, 
      date, 
      SUBSTRING_INDEX(SUBSTRING_INDEX(tags, ',', numbers.n), ',', -1) AS tag
  FROM 
      my_table
  CROSS JOIN (
      SELECT a.N + b.N * 10 + 1 n
      FROM 
          (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
      CROSS JOIN 
          (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
      ORDER BY n
  ) numbers
  WHERE 
      n <= 1 + LENGTH(tags) - LENGTH(REPLACE(tags, ',', '')) -- 确保只拆分必要的次数
) AS split_tags
WHERE 
    split_tags.date BETWEEN '2024-06-01' AND '2024-06-31' -- 更改日期范围以适应实际需求
GROUP BY split_tags.tag;