I used a subquery as a way round the problem (as follows) but is there a better solution?
Selecttables, count(*) 'count'
from(selectsubstring (so1.name, 1, 50)'tables'
fromsysobjectsso1
Whereso1.name like 'mf%'
Group By so1.name)tbl
group bytables
order bytables
Compute sum(count(*)) by tables
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“Doubt is not a pleasant condition, but certainty is absurd.” Voltaire