Multiple Aggregate functions with a group by clause - sql

Question

I have the following
WorkflowID FK_UA DateApprobation
----------- -------------------- -----------------------
1 3 NULL
2 1 NULL
3 1 NULL
4 2 2013-05-31 09:22:33.000
What I'm looking to do is to get a bunch of aggregate fields.
I want to get Approbated workflow , Non-Approbated workflow, All Workflows
The way I'm knowing that is if the "DateApprobation" field is null or has a value.
The thing is, I want to be able to group that by "FK_UA" so I don't know how to have 3 aggregate functions (COUNT) with a group by clause.
I'm looking for a query that can achieve that, I've tried a couple of similar case i found and it returned some weird values.
I tried this :
SELECT
FK_UA
,COUNT(WorkflowID) AS TOTAL
,COUNT(CASE when DateApprobation is not null then 1 else 0 end) AS APPROVED
,COUNT(CASE when DateApprobation is null then 1 else 0 end) AS NOT_APPROVED
FROM Workflow
GROUP BY
FK_UA
but it always return the same things for all 3 values!

Answer 1

SELECT
SUM(CASE WHEN [DateApprobation] IS NOT NULL THEN 1 ELSE 0 END) as [Approbated count],
SUM(CASE WHEN [DateApprobation] IS NULL THEN 1 ELSE 0 END) as [Non-Approbated count],
COUNT(*) as [Total]
FROM YourTable
GROUP BY FK_UA
If I got you right....

Answer 2

A standard SQL solution using COUNT()
You could have also used COUNT() but make sure you turn the values you don't want to count into NULL, not 0, as aggregate functions do not aggregate NULL values in SQL
SELECT
fk_ua,
COUNT(WorkflowID) AS total,
COUNT(CASE WHEN DateApprobation IS NOT NULL THEN 1 END) AS approved,
COUNT(CASE WHEN DateApprobation IS NULL THEN 1 END) AS not_approved
FROM Workflow
GROUP BY fk_ua
In fact, you could take this one step further in your case, because you're already counting the NOT NULL values:
SELECT
fk_ua,
COUNT(WorkflowID) AS total,
COUNT(DateApprobation) AS approved,
COUNT(WorkflowID) - COUNT(DateApprobation) AS not_approved
FROM Workflow
GROUP BY fk_ua
Or alternatively:
SELECT fk_ua, total, approved, total - approved AS not_approved
FROM (
SELECT
fk_ua,
COUNT(WorkflowID) AS total,
COUNT(DateApprobation) AS approved
FROM Workflow
GROUP BY fk_ua
) t
For large data sets, this might be slightly faster as your database should be able to recognise that there are only 2 distinct COUNT(...) expressions. Most commercial databases do.
A standard SQL solution using FILTER
Some SQL dialects, including e.g. PostgreSQL, implement the standard FILTER clause, which you can use to make things a bit more readable. Your query would then read:
SELECT
fk_ua,
COUNT(*) AS total,
COUNT(*) FILTER (WHERE DateApprobation IS NOT NULL) AS approved,
COUNT(*) FILTER (WHERE DateApprobation IS NULL) AS not_approved
FROM Workflow
GROUP BY fk_ua