As an alternative approach, you might avoid defining the query entirely and use a table/resource/field endpoint in Data Discovery. To update a single field of a single record simply send a PUT request to https://yourserver/db/CDHD/yourtable/id/1/pos_type, where id should be the table's primary key column and pos_type is the filed for updating.
The following example updates the BillingPostalCode field with value '456' for a record with InvoiceId = 1 in the Invoice table in the Chinook database.
curl https://demo.slashdb.com/db/Chinook/Invoice/InvoiceId/1/BillingPostalCode -XPUT -i -H 'Content-Type: application/json' -d '"456"'
If you need to update more than one field, make your request against the resource endpoint (individual record), and send JSON object as payload. Here's how to update both the BillingPostalCode and the BillngCountry fields for the same record at the same time:
curl https://demo.slashdb.com/db/Chinook/Invoice/InvoiceId/1 -XPUT -i -H 'Content-Type: application/json' -d '{"BillingPostalCode": "456" "BillingCountry": "Germany"}'
See docs: