SQL将结果分为2列

Question

I have a question about retrieving data using SQL

i want to get

count(comments_id) where comment_year = 2012 and 
count(comments_id) where comment_year = 2013 

in one query to get the output like this:

year12_comments  |  year13_comments
7                |  8         

I hope its clear.

Answer 1

Like this

...
SUM(CASE WHEN comment_year = 2012 THEN 1 ELSE 0 END) AS year12_comments,
SUM(CASE WHEN comment_year = 2013 THEN 1 ELSE 0 END) AS year13_comments,
...

---

Update:

If you want to get the percentage between them, you can enclose them in a subquery like this:

SELECT 
   (year12_comments / year13_comments) * 100
FROM
(
  SELECT
     ...
     SUM(CASE WHEN comment_year = 2012 THEN 1 ELSE 0 END) AS year12_comments,
     SUM(CASE WHEN comment_year = 2013 THEN 1 ELSE 0 END) AS year13_comments,
     ...

 ) sub

---

Update2

If you want to make the year12_comments, year13_comments as well as the percentage new column, just include them in the SELECT statement like this:

SELECT 
  year12_comments, 
  year13_comments,
  (year12_comments / year13_comments) * 100 AS ThePercenatge 
FROM
(
  SELECT
     ...
     SUM(CASE WHEN comment_year = 2012 THEN 1 ELSE 0 END) AS year12_comments,
     SUM(CASE WHEN comment_year = 2013 THEN 1 ELSE 0 END) AS year13_comments,
     ...

) sub

Answer 2

COUNT(CASE WHEN comment_year = 2012 THEN 1 END) year12_comments,
COUNT(CASE WHEN comment_year = 2013 THEN 1 END) year13_comments,

If you are using MS SQL Server 2005 or above, you can use PIVOT

Answer 3

Unless you can use the PIVOT function @HamletHakobyan suggested, IMHO this is a bad decision. Unless (another) end of the World happens in 2013, you'll have to do this for 2014 too. I'd rather go with a simple group by for the user and the year too:

SELECT user_id, comment_year, count(1)
FROM mytable
GROUP BY user_id, comment_year

Sure, you'll have to code a bit in your application, but from a clarity aspect, this seems to be the way to go...

(BTW I think this will be quicker than the CASE WHEN structure too...)