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The problematic brackets come from SqlSet(). You actually want just a single value, not a set of values:

SqlUpdate(LINK)(ID_OTHER, SqlSet(Select(ID_TWO).From(TWO).Where(NAME_TWO == "Name"))).Where(ID_LINK == 1);


This should work as you intended.

error C2664: 'Upp::SqlUpdate &Upp::SqlUpdate::operator ()(const Upp::SqlId &,Upp::SqlVal)' : cannot convert argument 1 from 'Upp::SqlId' to 'const Upp::SqlSet &'
Reason: cannot convert from 'Upp::SqlId' to 'const Upp::SqlSet'