DB2 SQL : Combine two queries and select max of one aggregate column -

i have 2 queries (example version)-

query a:

select    col1 col1,   col2 col2,   sum(col3) col3 table1 join table11 .. group col1, col2;

query b:

select    col1 col1,   col2 col2,   count(col3) col3 table2 group col1, col2;

i want join both of them , have output below. tried this

select a.col1, a.col2, greatest(a.col3, b.col3) (query a) union (query b) b

but getting error

sql0104n unexpected token "end-of-statement" found following "col2) b". expected tokens may include: "join <joined_table>". sqlstate=42601

both queries individually running fine, when combined using union above, giving error.

is there better way achieve this?

it looks need join, not union:

select a.col1, a.col2, greatest(a.col3, b.col3) (query a) join (query b) b on a.col1 = b.col1 , a.col2 = b.col2

depending on needs, may need left join, right join or full outer join instead of inner join.

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