如何只更新那些可整除的 MySQL

Question

update comments
set comment = case
    when id % 7 = 0 then 'The universe is such an amazing thing.'
    when id % 5 = 0 then 'I definitely read the article again.'
    when id % 3 = 0 then 'This is interesting.'
    when id % 2 = 0 then 'Very good article'
end
where id between 1 and 15;

它给了我错误：错误代码：1048。“评论”列不能为空！ 我只想更新那些可以整除的女巫。 所有其他不可分割的我想保持不变。

Answer 1

您可以将else 分支添加到case 表达式，当它不匹配任何除数时保持注释不变：

update comments
set comment = case
    when id % 7 = 0 then 'The universe is such an amazing thing.'
    when id % 5 = 0 then 'I definitely read the article again.'
    when id % 3 = 0 then 'This is interesting.'
    when id % 2 = 0 then 'Very good article'
    else comment
end
where id between 1 and 15;

或者您可以使用where 条件：

update comments
set comment = case
    when id % 7 = 0 then 'The universe is such an amazing thing.'
    when id % 5 = 0 then 'I definitely read the article again.'
    when id % 3 = 0 then 'This is interesting.'
    when id % 2 = 0 then 'Very good article'
end
where 
    id between 1 and 15
    and (id % 2 = 0 or id % 3 = 0 or id % 5 or id % 7 = 0)

如果您真的要过滤 1 到 15 之间的值，那么这可以简化：

 where id between 1 and 15 and id not in (1, 11, 13)

Answer 2

您的“案例”并未描述所有可能的案例。

13 不是 0 %7、%5、%3 也不是 %2。

最好的做法是添加一个default 案例来捕获这些场景，在 SQL 语言中标记为 else。