LOOKUPVALUE expects a single value in search column

[Zyg_D]

I try to do a measure that looks up for a value in a related table. I tried the LOOKUPVALUE solution, offered here. But my case should be slightly different, because I receive this error: 

"A single value for column 'ett_data_nuo' in table 'vwEtatas' cannot be determined. This can happen when a measure formula refers to a column that contains many values without specifying an aggregation such as min, max, count, or sum to get a single result."

It is exactly what it says, I have many identical values in vwEtatas[ett_data_nuo], but it is the column containing search values (not what I want to return), so I don't get why is it a problem. I want to return data from the table vwData where values from vwEtatas[ett_data_nuo] appear only once. 

[Zyg_D · Accepted solution]

I made it.

Not a measure but a new column. I think this was the key. Both formulas work now, but only as new columns, not measures. 

Another thing worth noting, I had to switch from DirectQuery to Import. As can be seen in the image, at first I did not have the "Data" tab available on left, where I can actually add new columns. 

colDataNuo = LOOKUPVALUE(vwData[dat_date],vwData[dat_id],vwEtatas[ett_data_nuo])
colDataNuo2 = MAXX(FILTER(vwData,vwData[dat_id]=vwEtatas[ett_data_nuo]),vwData[dat_date])

[amitchandak]

try

firstnonblank('vwEtatas'[ett_data_nuo],true)

[Zyg_D]

This returns data from my first table, not from the second (related) table. 

I tried

firstnonblank('vwData'[dat_date],true)

But this takes too long to calculate, I canceled the calculation after 30 mins without seeing the result. 

[amitchandak]

I usually create a new column like this

Max Sales order id = Maxx(filter(sales,Sales[item_id]='Item'[Item ID]),Sales[Order Id]) 

to get data from another table.