select sum(length(course)-length(replace(course,",",""))+1) as staff_nums

from cultivate_tb

where course is not null

新的知识点哈

1.length 计算字符数

2.replace 替换字符串中的内容

REPLACE(原始字符串, 要替换的文本, 替换后的文本)

还有个笨办法，通过union all 合并去计算