Canvas mapColumn and essql query

I'm wondering if it is possible to use an essql query in a mapColumn.
I try to make second column and want to use the value in the first column to check if it exists in another index by using an essql query.

But I can not get it working for now I only get Null values, and I don't know how to use the getCell in the essql statement:

| var_set name="hosts" value={essql query="select as targets from \"logs-scanner-scanlog\""}
| var name="hosts"
| mapColumn name="Critical" expression={ essql "select count(scanner.vcctarget) from \"reports-scanner-data\"" }
| table 
| render