sql - How to select the TOP 1 record per group (Partition) -


i've got table called tblroutes holds unique list of , routes (f = from; t = to):

| fcity  | fstate | tcity  | tstate | |========|========|========|========| |new york|   ny   | miami  |   ca   | |houston |   tx   |new york|   ny   | ...

and have table called tblcarrierrates lists bunch of tiers , rates offered carriers travelling routes:

| fcity  | fstate | tcity  | tstate | tier | rate | carrid |  carrname   | |========|========|========|========|======|======|========|=============| |new york|   ny   | miami  |   ca   |   2  | $2.99|  abcd  | abracadabra | |new york|   ny   | miami  |   ca   |   1  | $3.00|  bump  | bumpy rides | |houston |   tx   |new york|   ny   |   2  | $4.00|  slow  |slow carriers| |houston |   tx   |new york|   ny   |   2  | $4.01|  abcd  | abracadabra | ...

for each unique route listed in tblroutes i'm looking 1 "best" offered tblcarrierrates.

the criteria "the best" lowest tier, followed lowest rate.

the result needs return fields shown in tblcarrierrates, based on 2 routes shown above in tblroutes, desired result be:

| fcity  | fstate | tcity  | tstate | tier | rate | carrid |  carrname   | |========|========|========|========|======|======|========|=============| |new york|   ny   | miami  |   ca   |   1  | $3.00|  bump  | bumpy rides | |houston |   tx   |new york|   ny   |   2  | $4.00|  slow  |slow carriers|

the approach looking @ sort in ascending order tier , rate, how match top 1 record each unique combination of fcity, fstate, tcity, , tstate:

select a.fcity, a.fstate, a.tcity, a.tstate, q.tier, q.rate, q.carrid, q.carrname tblroutes left join      (select top 1 b.carrid, b.carrname, b.fcity, b.fstate, b.tcity, b.tstate, b.rate, b.tier     tblcarrierrates b     order tblcarrierrates.tier asc, tblcarrierrates.rate asc) q on (a.tstate = q.tstate) , (a.tcity = q.tcity) , (a.fstate = q.fstate) , (a.fcity = q.fcity);

the query doesn't fail, can guess, subquery i've written (q) returns single record rather 1 each route in tblroutes, end result is:

| fcity  | fstate | tcity  | tstate | tier | rate | carrid |  carrname   | |========|========|========|========|======|======|========|=============| |new york|   ny   | miami  |   ca   |   1  | $3.00|  bump  | bumpy rides | |houston |   tx   |new york|   ny   |      |      |        |             |

...as can see, nothing's been matched houston new york because sub query returned 1 result rather 1 each route.

how can achieve result i'm after?

i believe looking equivalent of sql server , oracle analytic / windowing functions row_number() on (partition .. order by), e.g. like so.

although isn't directly offered in ms access, believe possible simulate row numbering function in ms access applying correlated subquery counts number of rows have same "partition" (as defined join filter), , in each row ranked counting number of preceding rows in same partition, 'below' ordering criteria:

select a.fcity, a.fstate, a.tcity, a.tstate, q.tier, q.rate, q.carrid, q.carrname, therank tblroutes left join      (       select b.carrid, b.carrname, b.fcity, b.fstate, b.tcity, b.tstate, b.rate, b.tier,        (         select count(*) + 1          tblcarrierrates rnk          -- partition simulation (join)         b.fcity = rnk.fcity , b.fstate = rnk.fstate                , b.tcity = rnk.tcity , b.tstate = rnk.tstate                -- order simulation               , (rnk.tier < b.tier or                   (rnk.tier = b.tier , rnk.rate < b.rate))) therank       tblcarrierrates b) q on (a.tstate = q.tstate) , (a.tcity = q.tcity)      , (a.fstate = q.fstate) , (a.fcity = q.fcity) -- now, want top rank in each partition. therank = 1;

just forewarned of performance - subquery executed each row. also, if there ties, both rows returned.

the +1 start each partition off row number of 1 (since there 0 preceding rows in partition)

edit, taking out comments 

select a.fcity, a.fstate, a.tcity, a.tstate, q.tier, q.rate, q.carrid, q.carrname, therank tblroutes left join      (       select b.carrid, b.carrname, b.fcity, b.fstate, b.tcity, b.tstate, b.rate, b.tier,        (         select count(*) + 1          tblcarrierrates rnk          b.fcity = rnk.fcity , b.fstate = rnk.fstate                , b.tcity = rnk.tcity , b.tstate = rnk.tstate                , (rnk.tier < b.tier or                   (rnk.tier = b.tier , rnk.rate < b.rate))) therank       tblcarrierrates b) q on (a.tstate = q.tstate) , (a.tcity = q.tcity)      , (a.fstate = q.fstate) , (a.fcity = q.fcity) therank = 1

Comments

Post a Comment

Popular posts from this blog

c++ - Difference between pre and post decrement in recursive function argument -

i have following sample code used pre-decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(--c); cout << c << endl; return; } } this function give output input 4 : dp3 dp2 dp1 dp0 0 1 2 3 but when use post decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(c--); cout << c << endl; return; } } output goes in infinite loop dp4 can explain me in detail why happens ? this happens because function(c--) called same value of c , when finishes c decremented. recursively called, hence called same value no chance of return , hit stack overflow error. assume this, int x = 1, y = 0; y = x++ result y == 1 , x == 2. if y = ++x , bot x , y 2.
Read more

php - Nothing but 'run(); ' when browsing to my local project, how do I fix this? -

i added new project. made mistake in projectname.conf file in sites-available apache2, led me reinstalling apache2. after reinstalling , re-enabling projects on every page of every project .. <body> run(); </body> .. i've run composer update, restarted service, restarted pc, checked config files, tried disabling new project. there nothing in error log, , access.log: 127.0.0.1 - - [15/may/2015:01:40:47 +0200] "get / http/1.1" 304 181 "-" "mozilla/5.0 (x11; ubuntu; linux x86_64; rv:38.0) gecko/20100101 firefox/38.0" maybe i'm forgetting apache2 reinstall? don't think did different last time installed it. looks haven't setup php correctly. take @ this great guide , maybe you're forgetting link php config apache2.
Read more

php - How can I echo out this array? -

i don't know how go grabbing data in variable , put foreach loop. class tree{ private $info = array( array('name'=>'jim','state'=>'nu','company'=>'nu','phone'=>array('cell'=>'5615111111','office'=>'5611111111'),'email'=>array('primary'=>'exs@example.com','ex@there.com')), array('name'=>'joe smith','city'=>'phoenix','phone'=>'4805551111','email'=>'jsmith@some_email.com'), array('name'=>'john doe','city'=>'chandler','company'=>'doe co.','email'=>array('jdoe@gmail.com','personal'=>'email@email.com'),'phone'=>'6025550002') ); } if you're inside of class, can access private variable using $this->variablename . example, i...
Read more