SQL case when with equality and count conditions - sql

Question

How can i perform a query with filtering both value and count of the element.Such as
Select
(case
when element = 'data1' and (select count(element) from mytable where element='data1') > 15 then '1'
when element = 'data2' and (select count(element) from mytable where element='data2') > 15 then '2'
.
.
.
)
from mytable
where conditions
are there any quick and simple ways to implement this?

Answer 1

I think you want window functions:
select (case when element = 'data1' and
count(*) over (partition by element) > 15
then '1'
when element = 'data2' and
count(*) over (partition by element) > 15
then '2'
.
.
.
)
from mytable
where conditions

Answer 2

For both code clarity and performance reason, I would separate the aggregating in a CTE and then invoke it in a join. If the table is big perhaps make sense you put the result in a temporary table instead of CTE for performance reasons.
;WITH ElementCTE
AS
(
SELECT element, count(Element) AS count_Element
FROM mytable
GROUP BY element
WHERE Conditions
)
SELECT
CASE ELEMENT
WHEN 'Data1' AND count_Element > 15 THEN '1'
WHEN 'Data2' AND count_Element > 15 THEN '2'
FROM mytable AS mt
INNER JOIN Element AS el
ON mt.Element = el.Element
WHERE mt.conditions

Answer 3

Assuming you have a table:
CREATE TABLE NULLTEST
(
TransactioNo INT,
Code VARCHAR(25)
)
INSERT INTO NULLTEST VALUES (NULL, 'TEST1');
INSERT INTO NULLTEST VALUES (NULL, 'TEST2');
INSERT INTO NULLTEST VALUES (1, 'TEST2');
The query could look like this:
SELECT
CASE
WHEN Code = 'TEST2' AND
(SELECT COUNT(1) FROM dbo.NULLTEST n WHERE n.Code = 'TEST2')> 1 THEN '1'
WHEN Code = 'TEST1' AND
(SELECT COUNT(1) FROM dbo.NULLTEST n WHERE n.Code ='TEST1')> 1 THEN '2'
ELSE '3' end Yourcolumn
FROM dbo.NULLTEST t
WHERE ...