FW: Sequential scan

Is an index on paymonth necessary ? We had technical support out here at our site, and they requested that I drop all indexes on my system where the column of a stand-alone index is already the leading column in another composite index (for the same table of course). They said that we had alot of duplication where indexes were concerned and by duplicating the optimiser had more work to do, which could affect our performance. Any comments ? Dirk Reach Technologies -----Original Message----- From: owner-informix-list@iiug.iiug.org [mailto:owner-informix-list@iiug.iiug.org]On Behalf Of Mark Griebling Sent: Monday, January 29, 2001 5:41 PM To: shahid.mehmood; informix-list@iiug. org (E-mail) Subject: Re: Hi Shadid, You need an index on payprmbcalc.paymonth. Later, Mark At 05:58 PM 1/29/01 +0500, shahid.mehmood wrote: OS: SCO UNIX 5.0, IX: OWS 7.20.UC2 I have a table named payprmbcalc which also has index on its three fields. This table contains 28000+ records. when I run a query on this table with the db engine searches the table using sequential scan, where as I am expecting search using an index. this query is taking too long to complete. can you guys suggest any thing how to improve this query ... The table schema and 'set explain on' output is attached here with. The Table Schema ... { TABLE "paydba".payprmbcalc row size = 58 number of columns = 9 index size = 36 } create table "paydba".payprmbcalc ( paymonth integer not null constraint "paydba".n196_305, internalno char(6) not null constraint "paydba".n196_306, currency char(10) not null constraint "paydba".n196_307, balance decimal(10,2), product decimal(10,2), taxprofit decimal(10,2), ntaxprofit decimal(10,2), lastedit date, lastuser char(10) ); create unique index "paydba".pp001idx on "paydba".payprmbcalc (paymonth,internalno, currency); the 'set explain output' ... QUERY: ------ select employee.employeeno , payprmbcalc.internalno, employee.fname , employee.mname , employee.lname , payprmbcalc.currency , payprmbcalc.balance , employee.appointment , employee.termination , payprmbcalc.product , payprmbcalc.taxprofit , payprmbcalc.ntaxprofit from payprmbcalc, employee where payprmbcalc.paymonth = 2000130000 and employee.internalno = payprmbcalc.internalno order by 1 Estimated Cost: 7 Estimated # of Rows Returned: 5 Temporary Files Required For: Order By 1) paydba.payprmbcalc: SEQUENTIAL SCAN { why ? i need index scan } Filters: paydba.payprmbcalc.paymonth = 2000130000 2) paydba.employee: INDEX PATH (1) Index Keys: internalno Lower Index Filter: paydba.employee.internalno = paydba.payprmbcalc.internalno an early reply will be highly appreciated. thanks. Shahid Mehmood Software Designer & IX DBA Information Systems Department The Aga Khan University, Karachi Official: Yes

I agree with tech support ... There might be a few _extreme_ cases where I might have an index on a column which is aready the leading column of another index on that table. Will In article <955ppo$1ag$1@news.xmission.com>, "Dirk Moolman" <dirkm@reach.co.za> wrote: > > Is an index on paymonth necessary ? We had technical support out here at > our site, and they requested that I drop all indexes on my system where the > column of a stand-alone index is already the leading column in another > composite index (for the same table of course). > > They said that we had alot of duplication where indexes were concerned and > by duplicating the optimiser had more work to do, which could affect our > performance. > > Any comments ? > > Dirk > Reach Technologies > > -----Original Message----- > From: owner-informix-list@iiug.iiug.org > [mailto:owner-informix-list@iiug.iiug.org]On Behalf Of Mark Griebling > Sent: Monday, January 29, 2001 5:41 PM > To: shahid.mehmood; informix-list@iiug. org (E-mail) > Subject: Re: > > Hi Shadid, > > You need an index on payprmbcalc.paymonth. > > Later, > > Mark > > At 05:58 PM 1/29/01 +0500, shahid.mehmood wrote: > > OS: SCO UNIX 5.0, IX: OWS 7.20.UC2 > > I have a table named payprmbcalc which also has index on its three fields. > This > table contains 28000+ records. when I run a query on this table with the db > engine searches the table using sequential scan, where as I am expecting > search > using an index. this query is taking too long to complete. can you guys > suggest > any thing how to improve this query ... > > The table schema and 'set explain on' output is attached here with. > > The Table Schema ... > > { TABLE "paydba".payprmbcalc row size = 58 number of columns = 9 index size > = > 36 } > create table "paydba".payprmbcalc > ( > paymonth integer not null constraint "paydba".n196_305, > internalno char(6) not null constraint "paydba".n196_306, > currency char(10) not null constraint "paydba".n196_307, > balance decimal(10,2), > product decimal(10,2), > taxprofit decimal(10,2), > ntaxprofit decimal(10,2), > lastedit date, > lastuser char(10) > ); > > create unique index "paydba".pp001idx on "paydba".payprmbcalc > (paymonth,internalno, currency); > > the 'set explain output' ... > > QUERY: > ------ > select employee.employeeno , payprmbcalc.internalno, > employee.fname , employee.mname , employee.lname , > payprmbcalc.currency , payprmbcalc.balance , > employee.appointment , employee.termination , > payprmbcalc.product , payprmbcalc.taxprofit , > payprmbcalc.ntaxprofit > from payprmbcalc, employee > where payprmbcalc.paymonth = 2000130000 > and employee.internalno = payprmbcalc.internalno > order by 1> > Estimated Cost: 7 > Estimated # of Rows Returned: 5 > Temporary Files Required For: Order By > > 1) paydba.payprmbcalc: SEQUENTIAL SCAN { why ? i need index scan } > > Filters: paydba.payprmbcalc.paymonth = 2000130000 > > 2) paydba.employee: INDEX PATH > > (1) Index Keys: internalno > Lower Index Filter: paydba.employee.internalno = > paydba.payprmbcalc.internalno > > an early reply will be highly appreciated. > > thanks. > > Shahid Mehmood > Software Designer & IX DBA > Information Systems Department > The Aga Khan University, > Karachi > > Official: Yes > > Sent via Deja.com http://www.deja.com/