Re: Effective query for listing flags in use by messages in a folder

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From: Hector Vass <hector.vass@metametrics.co.uk>
To: Andreas Joseph Krogh <andreas@visena.com>
To: pgsql-sql@postgresql.org <pgsql-sql@postgresql.org>
Subject: Re: Effective query for listing flags in use by messages in a folder
Date: Thu, 19 Mar 2015 08:28:32 +0000
Message-ID: <1426753712227.33226@metametrics.co.uk> (raw)
In-Reply-To: <1426684757283.55625@metametrics.co.uk>
References: <1426683287617.19714@metametrics.co.uk>
	<VisenaEmail.35.3a752eb0ccc59659.14c2cf6ffdf@tc7-visena>
	<1426684757283.55625@metametrics.co.uk>
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If you cannot change the message table and only want something more elegant than union & limit 1 then could produce array of flags and unnest them ... dont know what performance would be like ... i


select
-- folder_id,
flags
from (
select
folder_id,
unnest(
array[
case when max(is_seen::int)=1 then 'is_seen' end,
case when max(is_replied::int)=1 then 'is_replied' end,
case when max(is_forwarded::int)=1 then 'is_forwarded' end,
case when max(is_deleted::int)=1 then 'is_deleted' end,
case when max(is_draft::int)=1 then 'is_draft' end,
case when max(is_flagged::int)=1 then 'is_flagged' end
]
) as flags
from message
group by 1
)x
where folder_id=1 and flags is not null;

?



Hector Vass



+44(0)7773 352 559
*  Metametrics, International House, 107 Gloucester Road,  Malmesbury, Wiltshire, SN16 0AJ
*   www.metametrics.co.uk<http://www.metametrics.co.uk/;

________________________________
From: pgsql-sql-owner@postgresql.org <pgsql-sql-owner@postgresql.org> on behalf of Hector Vass <hector.vass@metametrics.co.uk>
Sent: 18 March 2015 13:19
To: Andreas Joseph Krogh; pgsql-sql@postgresql.org
Subject: Re: [SQL] Effective query for listing flags in use by messages in a folder


My recommendation is to hold the data as key value pairs not as a table with columns for each flag..


Taking your table message ... and loading into this key value pair table messaage2..


drop type if exists myflags cascade;
create type myflags as enum('is_seen','is_replied','is_forwarded','is_deleted','is_draft','is_flagged');
drop table if exists message2;
create table message2(
    folder_id integer not NULL,
    msg varchar(200),
    is_flag myflags
);
insert into message2 select folder_id,msg,'is_seen' from message where is_seen is TRUE;
insert into message2 select folder_id,msg,'is_replied' from message where is_replied is TRUE;
insert into message2 select folder_id,msg,'is_forwarded' from message where is_forwarded is TRUE;
insert into message2 select folder_id,msg,'is_deleted' from message where is_deleted is TRUE;
insert into message2 select folder_id,msg,'is_draft' from message where is_draft is TRUE;
insert into message2 select folder_id,msg,'is_flagged' from message where is_flagged is TRUE;

select is_flag from message2 where folder_id=1 group by 1;
?
work=# select is_flag from message2 where folder_id=1 group by 1;
  is_flag
------------
 is_seen
 is_deleted
 is_replied
(3 rows)






Hector Vass



+44(0)7773 352 559
*  Metametrics, International House, 107 Gloucester Road,  Malmesbury, Wiltshire, SN16 0AJ
*   www.metametrics.co.uk<http://www.metametrics.co.uk/;

________________________________
From: pgsql-sql-owner@postgresql.org <pgsql-sql-owner@postgresql.org> on behalf of Andreas Joseph Krogh <andreas@visena.com>
Sent: 18 March 2015 13:01
To: pgsql-sql@postgresql.org
Subject: Re: [SQL] Effective query for listing flags in use by messages in a folder

På onsdag 18. mars 2015 kl. 13:54:50, skrev Hector Vass <hector.vass@metametrics.co.uk<mailto:hector.vass@metametrics.co.uk>>:

OK I get it ..



drop type if exists myflags cascade;
create type myflags as enum('is_seen','is_replied','is_forwarded','is_deleted','is_draft','is_flagged');
drop table if exists message;
create table message(
    folder_id integer not NULL,
    msg varchar(200),
    is_flag myflags
);
insert into message values
(1,'msg b','is_seen'),
(1,'msg c','is_seen'),
(1,'msg d','is_seen'),
(1,'msg d','is_replied'),
(1,'msg e','is_seen'),
(1,'msg e','is_replied'),
(1,'msg h','is_deleted')
;

Not quite; you have 2 entries, one for each flag, for "msg d". I must have one tuple per message in this table.

--
Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
andreas@visena.com<mailto:andreas@visena.com>
www.visena.com<https://www.visena.com;
[cid:part_F764646621869HEPVJS]<https://www.visena.com;

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