sql server - Equivalent of GETDATE() BETWEEN Two DateTime Fields where Both can be NULL -

-

is

select [id]       ,[dateonline] --nullable       ,[dateoffline] --nullable       ,[pageid]       ,[downloadid]       ,[weight]   [downloadpage]   getdate() between [dateonline] , [dateoffline]

equivalent to:

select [id]       ,[dateonline] --nullable       ,[dateoffline] --nullable       ,[pageid]       ,[downloadid]       ,[weight]   [downloadpage]   ([dateonline] null or [dateonline] <= getdate())   , ([dateoffline] null or [dateoffline] > getdate())

but catering nulls?

or there more elegant way of doing it?

where parentheses needed here?

thanks.

edit:

both [dateonline] , [dateoffline] of type datetime

if [dateonline] null logic "online now"

if [dateoffline] null logic "never go offline (once online)"

sorry, should have included in question begin with.

the author's second query net better performance if there no indexes on columns. if there indexes, that's no brainer... using coalesce disable index , table scan instead of index seek (very bad performance).

even if there aren't indexes on columns, "is null" return constant... whereas, in case of coalesce function, null values still need evaluated each time. if have table full of null dateonline , dateoffline, performance leak cannot ignored.

in case, can't think of reason why you'd use coalesce in case.

also, i'm guessing (since you're checking date range) 2 dates or nothing. have check 1 of dates.

 ([dateonline] null)  or getdate() between [dateonline] , [dateoffline]

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++ - Using OpenSSL in a multi-threaded application -

-
i have been writing soap client application in c++ on ubuntu using openssl https transport , pthreads threading. have number of threads - 1 central data acquisition thread periodically gets worker threads make soap requests via shared mutex protected queues. reading documentation openssl found is openssl thread-safe? in openssl faq describes mechanisms required ensure thread safety when using openssl. implemented , works fine. the reason question conceptual difficulty really. thinking implementing same functionality application has already, instead of using threads, create 2 seperate applications : 1 worker thread (of multiple copies running) , main data acquisition thread. use tcp sockets communicate between 2 rather mutex protected queues. may bad idea not important - confusing me would have implement same functions required ensure openssl thread safety in second approach or not? my guess not have , treated independent (indeed surely must many applications use openssl) re...
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