sql - PostgreSQL reusing computation result in select query -

-

for example using sql can do:

select (a+b) c table c < 5 , (c*c+t) > 100;

is there way using postgres?

this alternative might use:

select foo.c (     select (a+b) c table ) foo foo.c < 5  , (foo.c*foo.c+t) > 100

from performance point of view, think it's not optimal solution (because of lack of clause of foo subquery, hence returning table records). don't know if postgresql query optimization there.


Comments

Post a Comment

Popular posts from this blog

c# - SVN Error : "svnadmin: E205000: Too many arguments" -

-
i trying reposotries using c# code process svncommand = null; var psi = new processstartinfo("svnadmin"); psi.redirectstandardoutput = true; psi.redirectstandarderror = true; psi.useshellexecute = false; psi.arguments= @"dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump"; using (svncommand = process.start(psi)) { var myoutput = svncommand.standardoutput; var myerror = svncommand.standarderror; debug.write("output :" + environment.newline + environment.newline + myoutput.readtoend() + environment.newline + "error :" + environment.newline + environment.newline + myerror.readtoend()); svncommand.close(); } when use dump command commandline svnadmin dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump it works fine when try ...
Read more

c# - Copy ObservableCollection to another ObservableCollection -

-
how copy observablecollection item observablecollection without reference of first collection? here observablecollection item value changes affecting both collections. code private observablecollection<ratemodel> _allmetalrate = new observablecollection<ratemodel>(); private observablecollection<ratemodel> _metalrateondate = new observablecollection<ratemodel>(); public observablecollection<ratemodel> allmetalrate { { return this._allmetalrate; } set { this._allmetalrate = value; notifypropertychanged("metalrate"); } } public observablecollection<ratemodel> metalrateondate { { return this._metalrateondate; } set { this._metalrateondate = value; notifypropertychanged("metalrateondate"); } } foreach (var item in metalrateondate) allmetalrate.add(item); what causing , how can solve it? you need clone object referenced item before it's a...
Read more

All overlapping substrings matching a java regex -

-
is there api method returns (possibly overlapping) substrings match regular expression? for example, have text string: string t = 04/31 412-555-1235; , , have pattern: pattern p = new pattern("\\d\\d+"); matches strings of 2 or more characters. the matches are: 04, 31, 412, 555, 1235. how overlapping matches? i want code return: 04, 31, 41, 412, 12, 55, 555, 55, 12, 123, 1235, 23, 235, 35. theoretically should possible -- there obvious o(n^2) algorithm enumerates , checks substrings against pattern. edit rather enumerating substrings, safer use region(int start, int end) method in matcher . checking pattern against separate, extracted substring might change result of match (e.g. if there non-capturing group or word boundary check @ start/end of pattern). edit 2 actually, it's unclear whether region() expect zero-width matches. specification vague, , experiments yield disappointing results. for example: string line = "xx90xx"; strin...
Read more