Re: SQL question - Mailing list pgsql-novice
| From | Steve T |
|---|---|
| Subject | Re: SQL question |
| Date | |
| Msg-id | 1203405799.16875.235.camel@retsol610 Whole thread Raw |
| In response to | Re: SQL question ("Phillip Smith" <phillip.smith@weatherbeeta.com.au>) |
| List | pgsql-novice |
I was lead to believe that the benefit of JOINing tables was that you could explicitly state the criteria to be used - and hence the 'index'.
So
SELECT a.blah
FROM table1 AS a
JOIN table2 AS b
JOIN table3 AS c
ON c.foreignRecNo = b.recNo
ON b.foreignRecNo = a.recNo
explicitly says use the foreign key rec nos on table2 and table3 - where as
SELECT a.blah
FROM table1 AS a, table2 AS b, table3 AS c
WHERE b.foreignRecNo = a.recNo
AND c.foreignRecNo = b.recNo
would leave it up to the optimiser to decide the best route to the data.
Personally, since realising how JOIN works (and the JOIN syntax), I find that layout far easier to read as well - especially where you get convoluted where clauses such as:
WHERE table1.field1 = table3.field4
AND table2.field10 = table4.field2
AND table2.field7 = table4.field3
AND table2.field5 = table5.field1
AND table .....
where the 'joins' are on composite keys and the order of specification of the 'join' isn't necessarily intuitive.
On Tue, 2008-02-19 at 14:49 +1100, Phillip Smith wrote:
So
SELECT a.blah
FROM table1 AS a
JOIN table2 AS b
JOIN table3 AS c
ON c.foreignRecNo = b.recNo
ON b.foreignRecNo = a.recNo
explicitly says use the foreign key rec nos on table2 and table3 - where as
SELECT a.blah
FROM table1 AS a, table2 AS b, table3 AS c
WHERE b.foreignRecNo = a.recNo
AND c.foreignRecNo = b.recNo
would leave it up to the optimiser to decide the best route to the data.
Personally, since realising how JOIN works (and the JOIN syntax), I find that layout far easier to read as well - especially where you get convoluted where clauses such as:
WHERE table1.field1 = table3.field4
AND table2.field10 = table4.field2
AND table2.field7 = table4.field3
AND table2.field5 = table5.field1
AND table .....
where the 'joins' are on composite keys and the order of specification of the 'join' isn't necessarily intuitive.
On Tue, 2008-02-19 at 14:49 +1100, Phillip Smith wrote:
De: pgsql-novice-owner@postgresql.org [mailto:pgsql-novice-owner@postgresql.org] En nombre de Mag Gam Enviado el: Monday, February 18, 2008 5:37 PM Para: pgsql-novice@postgresql.org Asunto: [NOVICE] SQL question >> Is it better to use "JOIN" or comma method with equal sign when doing table joins? -----Original Message----- From: pgsql-novice-owner@postgresql.org [mailto:pgsql-novice-owner@postgresql.org] On Behalf Of Cesar Alvarez Sent: Tuesday, 19 February 2008 14:21 To: pgsql-novice@postgresql.org Subject: Re: [NOVICE] SQL question > It's better to use Join cause its easier to read the Sql statement I'm guessing there might be some effect on the planner as well maybe...? Someone smarter than me could shed some more light... THINK BEFORE YOU PRINT - Save paper if you don't really need to print this *******************Confidentiality and Privilege Notice******************* The material contained in this message is privileged and confidential to the addressee. If you are not the addressee indicated in this message or responsible for delivery of the message to such person, you may not copy or deliver this message to anyone, and you should destroy it and kindly notify the sender by reply email. Information in this message that does not relate to the official business of Weatherbeeta must be treated as neither given nor endorsed by Weatherbeeta. Weatherbeeta, its employees, contractors or associates shall not be liable for direct, indirect or consequential loss arising from transmission of this message or any attachments e-mail. ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
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