SQL Server联接到子查询

Question

I have a SQL Server table with call records and I'd like to get the number of calls in total and the total calls answered.

Here is what the table looks like:

 Extension | Status
 -----------------------
 300        Answered
 200        Not Answered
 ....       ...

What's the most efficient way to write a query that would return the extension, number of total calls (count on the entire table) and number of answered calls (count where Status = 'Answered' )?

I created a subquery and joined to it but it seems kind of inefficient so I have

    SELECT Extension, COUNT(*) AS total, answered.num as totalAnswered 
    FROM calls c INNER JOIN (SELECT Extension, COUNT(*) AS num FROM calls 
    WHERE Status = 'answered') answered ON c.Extension = answered.Extension
    GROUP BY Extension, answered.num

Thanks

Answer 1

SELECT DISTINCT Extension
    , COUNT(*) OVER() AS total
    , COUNT(*) OVER(PARTITION BY C.Extension) AS totalAnswered
FROM dbo.calls AS C
WHERE C.Status = 'answered';

You can use windows functions to achieve that. Should work just fine.

Answer 2

By using a case statement inside the count aggregate function for the total answered calls, you can keep your query very simple with a group by .

select extension,
       count(*) as total,
       count(case when status = 'answered' then 'X' end) as totalAnswered
  from calls
 group by extension

I am assuming you are trying to return totals per extension .

EDIT

I have to admit that your post in its current form is not 100% clear about your intent. The query you posted implies that you want the counts to be per extension . If that's the case, then the above query will work great.

But in the text of your post you say:

number of total calls (count on the entire table)

... which seems to imply something different: that you don't want the counts to per extension .

For completeness, here is the query you can use if you want the counts to be global to the entire table, instead of per extension :

select distinct extension,
                count(*) over () as total,
                count(case when status = 'answered' then 'X' end) over () as totalAnswered
  from calls

And, if for some reason, you need a combination of both kinds of counts, then you can use something like this:

  select extension,
         count(*) as totalPerExtension,
         count(case when status = 'answered' then 'X' end) as totalAnsweredPerExtension,
         totalGlobal,
         totalAnsweredGlobal
    from (select *,
                 count(*) over () as totalGlobal,
                 count(case when status = 'answered' then 'X' end) over () as totalAnsweredGlobal
            from calls) c
   group by extension, totalGlobal, totalAnsweredGlobal

Answer 3

SELECT Extention, 
       COUNT(*) as total, 
       SUM(answered) OVER (PARTITION BY Extention) as answered
FROM (
   SELECT Extention,
          CASE WHEN Status = 'answered' THEN 1 ELSE 0 END as answered
) T