Correct, it is a evaluating each row to see if it meets the condition (TRUE) or not (FALSE).
In your original post you indicated that you wanted a way to filter data using the select expert. I wrote the statement to be used in the select expert, not as a formula field.
I guess you are trying to use a formula field and then use that in the select statement which you can do but it really is adding in an extra step.
If you want to go down that rode then create a formula field as 'DataSelect' (or whatever you want):
if {FLATDATA_1.ACOD}} in ["TOC_","%ASH_C", "Next item here"] then "Sample Data" Else "QC Data"
I may have uinverted the data types above so just switch the order if you need to.
In your select statement you can then use
However this is the same thing as just making your select statement as:
{FLATDATA_1.ACOD}} in ["TOC_","%ASH_C", "Next item here"]