Measure that checks if a value in one table also exists in a second table

[Thomas_Qlik]

I want to build a table visualization that contains all the values from table/column  A.TO_BE and (in a second column) the output of a measure that checks, whether the value also exists in a second table/column B.AS_IS. If the value  exists in the second table, the MEASURE should return "OK", otherwise "NOK".  How would I do this in Qlik Sense?

Many thanks,

Thomas

Expected Output:

A.TO_BE | MEASURE

Apple       |    OK

Pear          |    OK

Cherry      |   NOK

Content of table A:

A.TO_BE

Apple

Pear

Cherry

Content of table B:

B.AS_IS

Apple

Pear

[Gabbar]

Add a table flag in both tables in script, or (There can be other columns in both table which you can use).
TableA:
Load A.TO_BE,'1' as Flag_A  from Source;
TableB:
Load B.AS_IS as A.TO_BE,'1' as Flag_B from Source;


then in your table in UI add A.TO_BE as Dimension, 
Add measure as 
If(Count({<Flag_A={'1'},Flag_B={'1'}>}A.TO_BE)>0,'OK','NOK')

IF you have columns in both table which can be used instead of flags you can do that do.

[Thomas_Qlik]

I have adjusted my code as instructed.  When I add the  A.TO_BE as Dimension, my table shows all 3  entries. But once I add the Measure, the entry that does not exist in the second table will disappear, instead of remaing in the table and showing 'NOK' as value in the Measure column.

[Gabbar · Accepted solution]

Use this :
if(aggr(Count({<Flag_A={1},Flag_B={1}>}A.TO_BE),[A.TO_BE])>0,'OK','NOK')

[Thomas_Qlik]

The formula produces the expected result.

Many thanks, Gabbar!