Convert SQL subquery to Power BI DAX - powerbi

Question

As a newbie of PowerBI, I was so struggled with this problem. I want to create a custom measure, and it can be solved easily with SQL statement which looks like this:
select count(*) from Task
where case_num in(
select case_num from Task
where task_type="DDD") sub
Can somebody help me with this. Thank you!!!!!
The table is roughly like this

Answer 1

You can isolate the case_nums that have a specific task type
VAR tbl = CALCULATETABLE(VALUES('Table'[case_num]),'Table'[task_type] = "DDD")
And then apply that table as a filter:
Measure =
VAR tbl = CALCULATETABLE(VALUES('Table'[case_num]),'Table'[task_type] = "DDD")
RETURN CALCULATE(COUNT('Table'[case_num]), TREATAS(tbl,'Table'[case_num]))
or
Measure =
VAR tbl = CALCULATETABLE(VALUES('Table'[case_num]),'Table'[task_type] = "DDD")
RETURN CALCULATE(COUNT('Table'[case_num]), 'Table'[case_num] IN tbl)

Answer 2

Try this measure
_count =
CALCULATE ( COUNT ( Task[CaseNum] ), FILTER ( Task, Task[task_type] = "DDD" ) )
Edit
If you have a small number of tasks which you want to use in filter, you can use this
Measure =
CALCULATE ( COUNT ( Task[Case] ), FILTER ( Task, Task[task_type] IN {"BB","AA","DDD","CC"}))
If you have a large number of tasks that you don't want to manually type in filter, then create a lookup table first and use that in a measure
TaskLookUpTable = DATATABLE ( --a long list of task; hence taskTbl
"task_type", STRING,
{
{ "BB"},
{ "AA"},
{ "DDD"},
{ "CC"}
}
)
Measure2 = --create the above table first before writing this measure
CALCULATE (
COUNT ( Task[Case] ),
TREATAS ( VALUES ( 'TaskLookUp'[task_type] ), Task[task_type] )
)