sql - SQL DB2：使用 min(date) 的意外结果

Question

这是有问题的脚本：

select distinct person, min(pdate) as min_date from db
where ptype like 'A1%'
or (ptype like 'B1%'
and (pdate between '2000-01-01' and '2001-01-01'))
group by person

问题

检索的 min_date 还包括我指定的日期之外的那些。但是，当我取出其中一种 ptype 时，我有：

select distinct person, min(pdate) as min_date from db
where ptype like 'A1%'
and (pdate between '2000-01-01' and '2001-01-01')
group by person

然后这个问题就消失了。为什么引入第二个 ptype 会重新调整我指定的更新之外的实例？

谢谢。

Answer 1

这是因为您现有的查询是以下形式：

IF A or (B and D)

- 所以如果 A 为真，则 D 被忽略。您实际上需要以下形式的查询：

IF (A or B) and D

像这样：

select distinct person, min(pdate) as min_date from db
where (ptype like 'A1%' or ptype like 'B1%') and 
      pdate between '2000-01-01' and '2001-01-01'
group by person

Answer 2

select distinct person, min(pdate) as min_date from db
where (      ptype like 'A1%'
         or (ptype like 'B1%'))
and (pdate between '2000-01-01' and '2001-01-01')
group by person

一）是假的？