Count if function in nested sql query - asp.net

Question

I have following query in sql server 2005 with a table
select t1.id, CONVERT(VARCHAR,t1.dt,103) date_1, CONVERT(VARCHAR,t2.dt,103) date_2, t1.hotel,
t1.price price_1, t2.price price_2, t2.price - t1.price difference, ((t2.price - t1.price)/t1.price)*100 as Diff_percentage
from test t1
inner join
(
select *
from test
) t2
on t1.hotel = t2.hotel
and t1.dt < t2.dt and t2.dt=(SELECT MAX(dt) from TEST) and t1.dt=(SELECT MAX(dt-1) from TEST)
I want to use count if function within this query. Based on difference column. So that i can count "How many increased, How many decreased, How many same, How many unavailable"
COUNT IF Difference>0 //How many increased
COUNT IF Difference<0 //How many decreased
COUNT IF Difference=0 //How many same
COUNT IF Difference="" //How many unavailable --Difference is blank.
DEMO : http://sqlfiddle.com/#!3/b6f37/29

Answer 1

If I wanted your existing query result I would rewrite the query as:
select t1.id,
CONVERT(VARCHAR,t1.dt,103) date_1,
CONVERT(VARCHAR,t2.dt,103) date_2,
t1.hotel,
t1.price price_1,
t2.price price_2,
t2.price - t1.price difference,
((t2.price - t1.price)/t1.price)*100 as Diff_percentage
from test t1
join (select max(dt) maxDt from test) d
on t1.dt = d.maxDt-1
join test t2
on t2.hotel = t1.hotel
and t2.dt = d.maxDt
To extend your original query to include hotels with missing rows:
select t1.id,
CONVERT(VARCHAR,t1.dt,103) date_1,
CONVERT(VARCHAR,t2.dt,103) date_2,
h.hotel,
t1.price price_1,
t2.price price_2,
t2.price - t1.price difference,
((t2.price - t1.price)/t1.price)*100 as Diff_percentage
from (select distinct hotel from test) h
cross join (select max(dt) maxDt from test) d
left join test t1
on t1.hotel = h.hotel
and t1.dt = d.maxDt-1
left join test t2
on t2.hotel = h.hotel
and t2.dt = d.maxDt
The above query would be much more efficient with a normalized HOTEL table (1 row per hotel) to replace the SELECT DISTINCT subquery.
To get your requested result, I would use:
select count(case when (t2.price-t1.price) < 0 then 1 end) decrease_count,
count(case when (t2.price-t1.price) > 0 then 1 end) increase_count,
count(case when (t2.price-t1.price) = 0 then 1 end) same_count,
count(distinct t1.hotel) - count(case when (t2.price-t1.price) is not null then 1 end) unavailable_count
from test t1
left join (select max(dt) maxDt from test) d
on t1.dt = d.maxDt-1
left join test t2
on t2.hotel = t1.hotel
and t2.dt = d.maxDt
Again the above would be more efficient with a normalized HOTEL table. I would restructure the query more like the previous one: select from HOTEL cross joined to the MAX date query, then outer join to the TEST table twice for the data for the 2 dates. The unavailable count could then be measured more directly, counting the number of rows where the difference computation is NULL.
Here is the SQL Fiddle for all the queries, along with some extended test data.

Answer 2

This approach uses your query and then just summarizes the results:
with t as (
select t1.id, CONVERT(VARCHAR,t1.dt,103) as date_1,
CONVERT(VARCHAR,t2.dt,103) as date_2,
t1.hotel,
t1.price as price_1, t2.price as price_2,
t2.price - t1.price as difference,
((t2.price - t1.price)/t1.price)*100 as Diff_percentage
from test t1 join
test t2
on t1.hotel = t2.hotel and
t1.dt < t2.dt and
t2.dt=(SELECT MAX(dt) from TEST) and
t1.dt=(SELECT MAX(dt-1) from TEST)
)
select sum(case when diff_percentage > 0.0 then 1 else 0 end) as numIncrease,
sum(case when diff_percentage < 0.0 then 1 else 0 end) as numDecrease,
sum(case when diff_percentage = 0.0 then 1 else 0 end) as numSame,
sum(case when diff_percentage is NULL then 1 else 0 end) as numBlank
from t
I'm not sure what "dt - 1" means. With date/datetime values in SQL Server, one usually uses "dateadd(day, -1, )" to subtract a date. In any case, there may be other ways to calculate what you want, but this answers your specific question.