How to match a drop down list with a single value from another column

[v_wadhawan]

Sir,
I have 2 tables: ‘DA11’ table with a list of 6 entries under [cat1] and 6 corresponding reference values in col 2 named [da1].
Other table"Pension"has 5 columns. In col named [category ] user has to select one of the items under [cat1]. I did this by valid if = DA11[cat1]. In the 2nd col of table “Pension” the user is automatically shown the value pertaining to his selection in [category]. by using valid if = DA11[da1]. this selects one of the 6 values matching with selected[category].
However, when I use SELECT(da11[da1],([_THISROW].[category] = [category]),TRUE), the user gets all the six values as given under da1 instead of single value . all the six values are shown even when I use SELECT(da11[da], [category]=[_THISROW].[category]) AND OTHER Select uses that I learnt.
I want to know whether use of select does not produce a single value that matches [category]?What other expressions are required to be used in such a scenario.
I am a learner and sorry for putting my query in a complicated manner.
thanks
vk

[Steve · Accepted solution]

Instead of this:

SELECT(da11[da1],([_THISROW].[category] = [category]),TRUE)

Try this:

SELECT(da11[da1],([_THISROW].[category] = [cat1]),TRUE)

[v_wadhawan]

Thanks a lot. It worked.
However, prior to your solution I tried SELECT(da11[da1], ([category]=[cat1]),True) and it also worked.
Whether it is required/more proficient to prefix the column [category] with [_THISROW] and what is the difference between the two and what damage if [_THISROW] is not used .
thanks again .

[Steve]

[_THISROW] is explained here:

FAQ: FILTER(), LOOKUP(), MAXROW(), MINROW(), REF_ROWS(), and SELECT() Tips & Tricks 💡

Back-references within nested queries ([_THISROW-n]) Consider a complex App formula with “nested” SELECT() expressions (SELECT() expressions within SELECT() expressions): SELECT( table[column1], ... SELECT( table[column2], ... SELECT( table[column3], ... ) ... ) ... ) Let’s call the row for which this entire expression is evaluated as its App formula the Origin Row. Within this entire expression, we can refer to column values of the Origin Row by dere…

The reason ([_THISROW].[category] = [category]) does’t work is because [category] isn’t a column in the da11 table. if AppSheet can’t find the column in the table, it looks for it in the row of the table performing the expression. As a result, this:

([_THISROW].[category] = [category])

was evaluated as though written like this:

([_THISROW].[category] = [_THISROW].[category])

which is always true.

It is because AppSheet tries to find the column when it isn’t sure that your attempt to use this worked:

SELECT(da11[da1], ([category]=[cat1]),True)

Because da11 doesn’t have [category], AppSheet evaluated the expression as if it were instead written like this:

SELECT(da11[da1], ([_THISROW].[category]=[cat1]),True)

So the use of [_THISROW] is optional when there’s no possibility of confusion over which column you mean.