mysql 求不同值，参考另外一列数据

Question

两列
uid,cookie

---

a12,zzzzz
null,zzzzz
a23,zzzzz
b34,ssss
null,ssss
请教各位大佬，数据如上，求uid个数，如果uid为null，则根据cookie统计，但是要与uid不为null的cookie去重。

Answer 1

写个大致意思吧：

select count(uid) from a where uid is not null + select count(1) from a where uid is null and cookie not in (select cookie from a where  uid is null)