Ordering problem with varchar (DESC) - from general ml. - Mailing list pgsql-admin

From Alexandre Leclerc
Subject Ordering problem with varchar (DESC) - from general ml.
Date
Msg-id 1dc7f0e30701310832r2da685d4ifd858f34373af84a@mail.gmail.com
Whole thread Raw
Responses Re: Ordering problem with varchar (DESC) - from general ml.  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-admin
Hi all,

I don't want to double post, but I see nothing hapening in the general
mailling list, so I post here in case any one has an idea about what
is going on.

We have a column (varchar) that has plain text time and it is indexed.
When I do a query with the index, all the data is in the right order,
but when I user ORDER BY .. DESC, the order is messed up. Example:

By index 1: (date, time, data)
SELECT * from t1;
date (date type)  time (varchar)  data
2007-01-17         8h40           d1
2007-01-30         9h30           d2
2007-01-30        12h00           d3
2007-01-30        13h45           d4
2007-01-30        17h20           d5

SELECT * from t1 ORDER BY date, time DESC;
date (date type)  time (varchar)  data
2007-01-30         9h30           d2
2007-01-30        17h20           d5
2007-01-30        13h45           d4
2007-01-30        12h00           d3
2007-01-17         8h40           d1

I don't know why, this is like if the 'time' varchar was trimmed then
used for the ordering.

How can I fix that so that the result is exactly like the first one but
perfectly reversed in it's order?

Best regards.

--
Alexandre Leclerc

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