Mysql group by 后面怎么加判断条件？

Question

有下面的 SQL 语句：

select count(*) from text_meta_ingest group by bool(clip_url_hash)

我希望可以统计 clip_url_hash 为：

• 为 null、
• 为 ''(空字符)
• 有实际值（长度大于 0）

这三种情况的 count，我应该怎么写？

Answer 1

用 case when 一劳永逸哦

select 
    d.checks, count(d.checks)
from (select (
    case clip_url_hash
    when '' then '空字符串'
    when null then 'NULL'
    else '正常的' end
) as checks from text_meta_ingest) as d
group by d.checks;

我测试的

Answer 2

就按你说的写啊，比如

select count(*) from text_meta_ingest group by IF(clip_url_hash is NULL, null, IF(clip_url_hash = '', '', 1));

嗯，你说的对...

select sum(if(core_chemical_code is null, 1, 0)) as totalNull, sum(if(core_chemical_code = '', 1, 0)) as totalEmpty, count(*) as total from text_meta_ingest

非空的行是 total - totalNull - totalEmpty