Re: [GENERAL] Why does this SQL work?
On Tue, May 12, 2015 at 04:07:52PM +0800, Anil Menon wrote: Thank you very much - looks like I will have to prefix all cols. You should anyway. Queries with unaliased columns make it impossible to analyze without in-depth knowledge of the database. Consider: select c1, c2, c3, c4, c5 from t1 join t2 using (c6) where c7 = 'a' and c8 now() and c9; which fields belong to which tables? what indexes make sense? it's impossible to tell. if the column references were prefixed with table name/alias - it would become possible, and easy, even, to figure out what's going on. depesz -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Why does this SQL work?
Thank you very much - looks like I will have to prefix all cols. Regards AK On Tue, May 12, 2015 at 3:05 AM, Victor Yegorov vyego...@gmail.com wrote: 2015-05-11 19:26 GMT+03:00 Anil Menon gakme...@gmail.com: manualscan= select count(*) From public.msgtxt where msgid in (select msgid From ver736.courier where org_id=3); count --- 10225 (1 row) Please note, there is no msgid col in courier table. Which brings the question why does this SQL work? An select msgid From courier where org_id=3 by itself gives error column msgid does not exist. Because you can reference both, inner and outer columns from the inner query. Here you're most likely referring to the outer `msgid` in the subquery. That's why it is always a good idea to prefix all your columns with tables aliases. -- Victor Y. Yegorov
Re: [GENERAL] Why does this SQL work?
2015-05-11 19:26 GMT+03:00 Anil Menon gakme...@gmail.com: manualscan= select count(*) From public.msgtxt where msgid in (select msgid From ver736.courier where org_id=3); count --- 10225 (1 row) Please note, there is no msgid col in courier table. Which brings the question why does this SQL work? An select msgid From courier where org_id=3 by itself gives error column msgid does not exist. Because you can reference both, inner and outer columns from the inner query. Here you're most likely referring to the outer `msgid` in the subquery. That's why it is always a good idea to prefix all your columns with tables aliases. -- Victor Y. Yegorov
Re: [GENERAL] Why does this SQL work?
On Tue, May 12, 2015 at 12:26:15AM +0800, Anil Menon wrote: manualscan= select count(*) From msgtxt where msgid in ( manualscan( select msgid From courier where org_id=3 manualscan( ) manualscan- ; count --- 10225 (1 row) manualscan= select count(*) From public.msgtxt where msgid in (select msgid From ver736.courier where org_id=3); count --- 10225 (1 row) Please note, there is no msgid col in courier table. Which brings the question why does this SQL work? An select msgid From courier where org_id=3 by itself gives error column msgid does not exist. This works because this is correlated subquery. You should have always use aliases to avoid such errors. Like here: select count(*) From msgtxt as m where m.msgid in ( select c.msgid from courier c where c.org_id = 3 ); Your query is equivalent to: select count(*) From msgtxt as m where m.msgid in ( select m.msgid from courier c where c.org_id = 3 ); which returns all rows from msgtxt if there is at least one row in courier with org_id = 3. depesz -- The best thing about modern society is how easy it is to avoid contact with it. http://depesz.com/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
[GENERAL] Why does this SQL work?
Hi,
I have the following setup :
manualscan= set search_path=ver736,public;
SET
manualscan= \d courier;
Table ver736.courier
Column | Type |Modifiers
---++--
org_id| smallint | not null default
nextval('courier_org_id_seq'::regclass)
courier_name | character varying(500) | not null
courier_code | character varying(50) |
is_valid | boolean|
universe_id | character varying(50) |
courier_image | bytea |
Indexes:
courier_pk PRIMARY KEY, btree (org_id)
courier_code_un UNIQUE CONSTRAINT, btree (courier_code)
courier_name_un UNIQUE CONSTRAINT, btree (courier_name)
courier_code_idx btree (courier_code)
Referenced by:
xxx...xxx...(a few tables)
manualscan= \d msgtxt;
Table public.msgtxt
Column | Type |
Modifiers
---+--+
msgid | integer | not null default
nextval('msgtxt_msgid_seq'::regclass)
msgval| text |
transaction_stamp | timestamp with time zone | default now()
corelationid | text |
deviverymode | integer |
destination | text |
expiration| integer |
messageid | text |
priority | integer |
redelivered | boolean |
replyto | text |
timestamp | bigint |
msgtype | text |
senderid | text |
Indexes:
msgtxt_pkey PRIMARY KEY, btree (msgid)
Triggers:
manual_scan_tx_tr AFTER INSERT ON msgtxt FOR EACH ROW EXECUTE PROCEDURE
process_manual_scan_tx()
manualscan= select count(*) From msgtxt where msgid in (
manualscan( select msgid From courier where org_id=3
manualscan( )
manualscan- ;
count
---
10225
(1 row)
manualscan= select count(*) From public.msgtxt where msgid in (select
msgid From ver736.courier where org_id=3);
count
---
10225
(1 row)
Please note, there is no msgid col in courier table. Which brings the
question why does this SQL work? An select msgid From courier where
org_id=3 by itself gives error column msgid does not exist.
OS Version : Centos 7
PG Version : PostgreSQL 9.4.1 on x86_64-unknown-linux-gnu, compiled by gcc
(GCC) 4.8.2 20140120 (Red Hat 4.8.2-16), 64-bit
Regards
AK
