syntax error in Data Explorer

问题

The Stack Exchange Data Explorer allows SQL queries against a Stack Exchange database. I tried this one —

select
  month(CreationDate) month,
  year(CreationDate) year,
  sum(lower(left(Title,2))='wh')/count(*) wh,
  (select sum(Score)/count(*)
   from Posts u
   where month(CreationDate)=month(t.CreationDate)
     and year(CreationDate)=year(t.CreationDate)
     and lower(left(Title,2))='wh'
     and PostTypeId=1 -- question
  ) wh_score,
  sum(Score)/count(*) score,
  (select sum(AnswerCount)/count(*)
   from Posts u
   where month(CreationDate)=month(t.CreationDate)
     and year(CreationDate)=year(t.CreationDate)
     and lower(left(Title,2))='wh'
     and PostTypeId=1 -- question
  ) wh_answers,
  sum(AnswerCount)/count(*) answers
from Posts t
where PostTypeId=1 -- question
group by month,year;

— but the site told me

Incorrect syntax near ')'. Incorrect syntax near 'wh_score'. Incorrect syntax near 'wh_answers'.

and I cannot figure out why. Can anyone help, please?

---

Things I've tried, to no avail:

• datepart(month,CreationDate) instead of month(CreationDate) (and likewise for year)
• explicit as for aliases (then the latter two of the three errors complained about 'at' rather than about the aliases)
• aliases that aren't built-in function names
• left(Title,2) instead of lower(left(Title,2))
• putting parentheses around the first two, and around the last two, of the four things joined by ands
• explicit u. for column names in the subqueries

回答1:

1. You can't group by an alias, you need to specify the computed column
2. This is not allowed : sum(lower(left(Title,2))='wh'). You have to convert it into a CASE WHEN operator.

Here a corrected query (that gives a timeout):

select
    month(CreationDate) month
  , year(CreationDate) year
  , sum(case when lower(left(Title,2))='wh' then 1 else 0 end)/count(*) wh
  , (select sum(Score)/count(*)
   from Posts u
   where month(CreationDate)=month(t.CreationDate)
     and year(CreationDate)=year(t.CreationDate)
     and lower(left(Title,2))='wh'
     and PostTypeId=1 -- question
  ) wh_score,
  sum(Score)/count(*) score,
  (select sum(AnswerCount)/count(*)
   from Posts u
   where month(CreationDate)=month(t.CreationDate)
     and year(CreationDate)=year(t.CreationDate)
     and lower(left(Title,2))='wh'
     and PostTypeId=1 -- question
  ) wh_answers,
  sum(AnswerCount)/count(*) answers
from Posts t
where PostTypeId=1 -- question
group by month(CreationDate), year(CreationDate);

What are you trying to do with this query?

来源：https://stackoverflow.com/questions/16076593/syntax-error-in-data-explorer