How can we select duplicate records from a table

Question

Hi
I desire to use a query to select duplicate columns (based on all the columns of the table) ...
I am able to write queries which include column names, but when my table contains more than 50 columns, is it advisable for me to mention all the 50 column names in the query or is there any other query by which duplicate rows can be selected without column names being mentioned ?
Thnx in advance
Regards

Answer 1

Basic rule of relational design says that "thy table shalt have a primary key".
Now assuming that you do not have a primary key constraint and that resulted in duplicates, you should still have a couple of columns that uniquely describes a row in that table.
To select duplicate rows can then be done by joining rows with the primary key (same set of unique columns), where rows have different rowids (physical addresses).
E.g.
select
t1.*,
t2.*
from table t1,
table t2
where t1.col1 = t2.col1
and t1.col2 = t2.col2
and t1.rowid < t2.rowidIf you do not have a couple of columns (primary key) that uniquely identifies a row, then you do not have duplicates in the table - as there cannot be duplicates without having a means of unique identification.