Question

The database type is PostGres 8.3.

If I wrote:

SELECT field1, field2, field3, count(*)  FROM table1 GROUP BY field1, field2, field3 having count(*) > 1; 

I have some rows that have a count over 1. How can I take out the duplicate (I do still want 1 row for each of them instead of +1 row… I do not want to delete them all.)

Example:

1-2-3 1-2-3 1-2-3 2-3-4 4-5-6 

Should become :

1-2-3 2-3-4 4-5-6 

The only answer I found is there but I am wondering if I could do it without hash column.

Warning I do not have a PK with an unique number so I can’t use the technique of min(…). The PK is the 3 fields.

Answer 1

This is one of many reasons that all tables should have a primary key (not necessarily an ID number or IDENTITY, but a combination of one or more columns that uniquely identifies a row and which has its uniqueness enforced in the database).

Your best bet is something like this:

SELECT field1, field2, field3, count(*)  INTO temp_table1 FROM table1 GROUP BY field1, field2, field3 having count(*) > 1  DELETE T1 FROM table1 T1 INNER JOIN (SELECT field1, field2, field3       FROM table1       GROUP BY field1, field2, field3 having count(*) > 1) SQ ON             SQ.field1 = T1.field1 AND             SQ.field2 = T1.field2 AND             SQ.field3 = T1.field3  INSERT INTO table1 (field1, field2, field3) SELECT field1, field2, field3 FROM temp_table1  DROP TABLE temp_table1