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:

You can't group by an alias, you need to specify the computed column
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

标签

sql

syntax-error

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