sql - Difference between NULL and Blank Value in Mysql -


i have check value of particular column named result blank or not.

when check if result null, query failed, when checked result='', worked.

what difference between two.

please explain.

"update rls_tp_2012_03 a, rls_tp_2012_03 b set a.comment=b.comment b.tcode='t1199' ,  a.groupname='xyz' , a.hlabno=b.hlabno , a.result =''; ";    "update rls_tp_2012_03 a, rls_tp_2012_03 b set a.comment=b.comment b.tcode='t1199' ,  a.groupname='xyz' , a.hlabno=b.hlabno , a.result null; "

  1. null absence of value. empty string value, empty. null special database.

  2. null has no bounds, can used string, integer, date, etc. fields in database.

  3. null isn't allocated memory, string null value pointer pointing in memory. however, empty allocated memory location, although value stored in memory "".


Comments

Post a Comment

Popular posts from this blog

javascript - RequestAnimationFrame not working when exiting fullscreen switching space on Safari -

request animation frame stops working when exiting fullscreen clicking on original space's safari window. fine if fullscreen mode canceled escape key or calling cancelfullscreen(). steps reproduce: open https://dl.dropboxusercontent.com/u/769042/prezi/safari-fullscreen.html click "draw raf", kittie appears click "fullscreen", go fullscreen click "draw raf", kittie appears go space original safari was, showing "click exit fullscreen mode", click anywhere, out fullscreen click "draw raf", nothing happens what handling click calling: window.requestanimationframe(draw); which draws on canvas context: function draw() { ctx.drawimage(img, math.random()*500|0, math.random()*400|0, 100, 100); } i checked .hidden , .visibilitystate, updated correctly. tested on osx 10.9.3, safari 7.0.4 (9537.76.4). has workaround/solution other switching old settimeout? this sounds webkit bug 88940 : using reque
Read more

Python ctypes access violation with const pointer arguments -

i have api i'm trying wrap in python (2.7.6 on win7) code using ctypes. here's api: client_dllfunc bool clientapi search_exporttoclipcopy(clienthsearch handle, int channel, lpctstr filename, const time_t& from, const time_t& to, const bool* cameras, int length, bool usepassword, lpctstr password, bool includetextin = false, bool excludeplayer = false); the issue i'm having cameras argument; , i've had issue other const pointer arguments well. here's how i'm wrapping api: def search_exporttoclipcopy(self, hsearch, csearch, filename, tfrom, tto, cameras, length, usepassword, password, includetextin=true, excludeplayer=false): exporttoclipcopy = self.sdkdll.search_exporttoclipcopy exporttoclipcopy.argtypes = [c_int, c_int, c_wchar_p, c_long, c_long, pointer(c_bool), c_int, c_bool, c_wchar_p, c_bool, c_bool] exporttoclipcopy.restype = c_bool exporttoclipcopy(hsearch, csearch, filename, tfrom, tto, cameras, length, usepassword, pass
Read more