Duplicates

Checking for duplicates

Any of these will identify values appearing more than once:

1. GROUP BY and HAVING

   select col1,count(*)
     from table_name a
    where ...
    group by col1
   having count(*) > 1;
   

2. Correlated subquery

   select col1
     from table_name a
    where ...
      and 1 < (select count(*)
                 from table_name b
                where b.col1 = a.col1);
   

3. CSQ to predicate EXISTS

   select col1
     from table_name a
    where ...
      and exists
          (select 'x'
             from table_name b
            where b.col1 = a.col1
              and b.rowid != a.rowid);