具体的sql怎么写？统计图片的总个数，不是统计有图片的数据的个数，并且一个字段下可能包含多个图片

假设图片数据保存在表`images`中，每个图片对应一条记录，包含一个字段`image_url`保存图片的URL。而这些图片是和其他数据相关联的，保存在表`related_data`中，每个记录包含一个字段`id`作为主键，并且还包含一个字段`image_urls`，保存相关联数据所包含的所有图片URL，多个URL之间用逗号分隔。

要统计所有图片的总个数，可以使用如下SQL语句：

SELECT COUNT(*) AS total_images FROM (
    SELECT image_url FROM images
    UNION ALL
    SELECT TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(t.image_urls, ',', n.n), ',', -1)) AS image_url
    FROM related_data t
    CROSS JOIN (
        SELECT a.N + b.N * 10 + 1 AS 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) AS 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) AS b
        ORDER BY n
    ) n
    WHERE n.n <= 1 + (LENGTH(t.image_urls) - LENGTH(REPLACE(t.image_urls, ',', '')))
) AS all_images;

这条SQL语句使用了UNION ALL和字符串分割函数来将两个来源的图片URL合并到一起，然后使用COUNT函数统计总数。具体来说：

- 子查询`SELECT image_url FROM images`选取所有的图片URL；
- 子查询`SELECT TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(t.image_urls, ',', n.n), ',', -1)) AS image_url FROM related_data t`选取所有相关联数据包含的图片URL，这里使用了两次SUBSTRING_INDEX函数来分割逗号分隔的字符串，再使用TRIM函数去掉可能存在的空格；
- 子查询`SELECT a.N + b.N * 10 + 1 AS 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) AS 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) AS b ORDER BY n`是一个生成连续数字序列的查询，用于在字符串分割时获取所有可能的位置；
- 子查询`SELECT COUNT(*) AS total_images FROM (...) AS all_images`对合并后的图片URL进行COUNT统计，使用AS语句给子查询取别名以方便引用。