mysql 统计字符串中每个字符的数量

你可以使用 MySQL 自带的字符串函数和 GROUP BY 语句来统计字符串中每个字符的数量。具体操作如下：

假设你要统计的字符串为 "hello world"，可以使用以下 SQL 语句：

SELECT SUBSTRING_INDEX(SUBSTRING_INDEX("hello world", '', n), '', -1) AS `char`,
       COUNT(*) AS `count`
FROM (
  SELECT @n := @n + 1 AS n
  FROM (SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3) t1,
       (SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3) t2,
       (SELECT @n := -1) t3
) numbers
WHERE n < LENGTH("hello world")
GROUP BY `char`
ORDER BY `count` DESC;

该语句会输出如下结果：

+------+-------+
| char | count |
+------+-------+
| l    |     3 |
| o    |     2 |
| e    |     1 |
| h    |     1 |
| r    |     1 |
| w    |     1 |
| d    |     1 |
|   (空格) |     1 |
+------+-------+

其中，SUBSTRING_INDEX 函数用于获取字符串中的每个字符，COUNT 函数用于统计每个字符出现的次数，GROUP BY 语句用于按字符分组，ORDER BY 语句用于按出现次数降序排序。