I'm not sure where you're getting your information ("Typically, db vendors
recommend you use an exists clause, not a join when testing for the presence
of child data because it's faster"). Not to say that you're incorrect, just
that in working for years with MS-SQL and Oracle and before that Sybase, I
have never seen such advice.
I just opened Query Analyzer to compare two queries similar to yours (in
MS-SQL).
Table sizes:
Customers: 50151
SalesTravellers: 51195
Q1:
select surname, givenName
from salestravellers
where not exists(
select 1 from customers
where salestravellers.customerid = customers.customerid)
Q2:
select salestravellers.surname, salestravellers.givenName
from salestravellers left join customers
on salestravellers.customerid = customers.customerid
where customers.customerid is null
For both queries:
Rows returned: 2751
Time for Q1: 0:0:02
Arthur
-----Original Message-----
From: Greg Matthews [mailto:greg55@stripped]
Sent: Monday, November 11, 2002 7:38 AM
To: mysql@stripped
Subject: Re: RE: MySql 4.1 Sub Selects and not stored procedures
hey, can i hijack my message back?...this thread is about the performance of
subselects, not stored procedures. go write your own message :-)...
so....the original question is if someone would be nice enough to answer..
====> Do any MySql coders writing subselects in 4.1 know whether EXISTS will
outperform an equivalent query written as a join. <=====
Typically, db vendors recommend you use an exists clause, not a join when
testing for the presence of child data because it's faster.
e.g.
4.1 version (faster?)
---------------------
select person.person_id, person.name from person where exists ( select 1
from invoice where invoice.paid is null and invoice.person_id =
person.person_id)
vs
4.0 version (slower?)
----------------------
select DISTINCT person.person_id, person.person_name from person, invoice
where person.person_id = invoice.person_id and invoice.paid is null
Thanks,
Greg.
----- Original Message -----
From: "Dan Rossi" <daniel@stripped>
To: "Victoria Reznichenko" <victoria.reznichenko@stripped>;
<mysql@stripped>
Sent: Monday, November 11, 2002 11:04 PM
Subject: RE: RE: MySql 4.1 Sub Selects
> damn , i read it was 4.1 i guess we have to wait a bit then, i wish i
could
> program some c ++ to hurry it along a bit, i dont really have access to
DB's
> like oracle to learn stored procedure stuff
>
> -----Original Message-----
> From: Victoria Reznichenko [mailto:victoria.reznichenko@stripped]
> Sent: Monday, November 11, 2002 11:00 PM
> To: mysql@stripped
> Subject: re: RE: MySql 4.1 Sub Selects
>
>
> daniel,
> Monday, November 11, 2002, 3:51:25 AM, you wrote:
>
> d> will 4.1 hopefully have stored procedure functionality ?
>
> Nope.
> Stored procedures will be implemented around v5.0
>
>
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