Thx for the replies - and apologies for delay in getting back to you.

Dennis - yes this is (mainly) correct

• 2 Servers X, Y
• c 45 Databases
• 2 Availability Groups...

Ant-Green,

thx for the response.

unfortunately no, not just reading from DBs in SProcs .... some do but most need a I/U/D ability

Dennis,

many thx for the response.

yes, points 1-3 are correct. DBs split into 2 AG groups on 2 servers - so on one server AG1 is primary and AG2 is secondary,...

Thx for the suggestions.
am on SQL 2016.

have got a working solution - and it appears to scale
Code was

         SELECT 
          mainT. Column1