In response to Chris Velevitch :
> I'm to write a query like:-
>
> select
> case when column_name1 <> value_of_previous(column_name1)
> then column_name1 end as column
> ,column_name2
> from table
> ordered by column_name1, column_name2
Okay, with this table:
test=# select * from foo;
col1 | col2
------+------
1 | 1
1 | 2
1 | 3
2 | 4
2 | 5
2 | 6
2 | 7
3 | 8
4 | 9
5 | 10
(10 rows)
you can do:
test=# select
case when col1::text <> coalesce(lag::text,'NULL') then col1 else null end as col1,
col2
from (
select col1, lag(col1) over (range unbounded preceding ),
col2
from foo
order by col2
) foo order by col2;
col1 | col2
------+------
1 | 1
| 2
| 3
2 | 4
| 5
| 6
| 7
3 | 8
4 | 9
5 | 10
(10 rows)
>
> How do I do this? (I'm using pg 7.4)
Unfortunately (for you), i'm using a window-function, in this case
lag(), new since 8.4. Your version 7.4 has reached End-of-Lifetime, so
i suggest you update to 8.4.
Regards, Andreas
--
Andreas Kretschmer
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