I just found the answer:

1. use as usual using {}, like select * from {entity1}

2. It confused as if i use SQL sandbox - it should be either using:

USE [db-name]

select *..

--- or

using syntax copied from Executed SQL drown from we join using aggregate

in this case no USE is needed

Warning:

DO NOT use this copied syntax in the Advance Query because there will error:

like prefix... blabla is reserved word...

Best practice:

# create aggregate join

# copy the ''executed sql" and push in the SQL Sandbox forge

# in  the advance query - replace the from table... use {entity} instead of the fully name

# try it

regards