如何计算 SQL 服务器中带有 where 子句的行数？

Question

I am pretty much stuck with a problem I am facing with SQL Server. I want to show in a query the amount of times that specific value occurs. This is pretty easy to do, but I want to take it a step further and I think the best way to explain on what I am trying to achieve is to explain it using images.

I have two tables: Plant and Chest

As you can see with the chest the column 'hoeveelheid' tells how full the chest is, 'vol' == 1 and 3/4 is == 0,75. In the plant table there is a column 'Hoeveelheidperkist' which tells how much plants there can be in 1 chest.

select DISTINCT kist.Plantnaam, kist.Plantmaat, count(*) AS 'Amount'
from kist

group by kist.plantnaam, kist.Plantmaat

This query counts all the chests, but it does not seperate the count of 'Vol' chests and '3/4' chests. It only does This . What I want to achieve is this . But I have no idea how. Any help would be much appreciated.

Answer 1

If you use group by you don't need distinct
and if you want the seprated count for hoeveelheid you ust add to the group by clause

    select DISTINCT kist.Plantnaam, kist.Plantmaat, kist.hoeveelheid, count(*) AS 'Amount'
    from kist
    group by kist.plantnaam, kist.Plantmaat, hoeveelheid

or if you want all the 3 count ond the samw rowx you could use a condition aggreagtion eg:

    select DISTINCT kist.Plantnaam, kist.Plantmaat
     , sum(case when kist.hoeveelheid ='Vol' then 1 else  0 end) vol 
     , sum(case when kist.hoeveelheid ='3/3' then 1 else  0 end) 3_4 
     , count(*) AS 'Amount'
    from kist
    group by kist.plantnaam, kist.Plantmaat

Answer 2

When you want to filter the data on the counts you have to use having clause. When ever you are using aggregate functions(sum, count, min, max) and you want to filter them on aggregation basis, use having clause

select DISTINCT kist.Plantnaam, kist.Plantmaat, count(*) AS 'Amount'
from kist

group by kist.plantnaam, kist.Plantmaat having count(*) = 1 -- or provide necessary conditions