SQL query for zero or more than 1 row

Question

have 2 tables Table1 and Table2
Table1 contains one varchar2 column Col1 with values: id1, id2, id3, id4, .....id9
Table2 contains two varchar2 columns with values:
Col1     Col2
id1     some1
id1     some2
id3     some3
id4     some4
id9     some5
id9     some6
Table1 and Table2 join on Table1.col1 = Table2.col1
I want to find those rows in Table1 that have zero or more than one values in Table2
So the output in the above case would be
id1 (since it has more than one corresponding values in Table2)
id2 (since it does not have corresponding value in Table2)
id9 (since it has more than one corresponding values in Table2)

Answer 1

One way:
select table1.col1
from table1 left outer join table2 on table1.col1 = table2.col1
group by table1.col1 having count(table2.col1) != 1
Where there is no match, table2.col1 in the outer join will be null, so the count will be zero.
Where there are multiple matches the count will be > 1.
Untested because you didn't supply table and data creation scripts. See Re: 2. How do I ask a question on the forums?