Question

Consider the following table:

primaryKey   id    activity   template  creator   created
1            1      3           5         x       2011-10-13
2            2      4           2         y       2011-10-15  
3            2      4           7         z       2011-10-24
4            2      4           7         u       2011-10-29

From here I want to retrieve the records which are having unique combinations for id, activity and template. In case there are two or more unique combinations of those fields are exists I want to take the first one of them.

As an example for above table data the output that I need is

primaryKey   id    activity   template  creator  created
1            1      3           5         x       2011-10-13
2            2      4           2         y       2011-10-15  
3            2      4           7         z       2011-10-24

(since record 3 and 4 are having same combination I want to take just the record 3 because it is the first occurance)

Can I do this using a single SQL statement?

Answer 1

SELECT primarykey, id, activity, template, creator, created FROM (
    SELECT *, row_number() OVER (partition BY id, activity, template ORDER BY created) as rn FROM table
) a 
WHERE rn = 1