sql server - Unique Constraint in SQL with Multiple NULL Values -

-

i read way ensure unique values in column in sql while allowing multiple nulls.

done using filtered indexes:

create unique index indexname on tablename(columns) include includecolumns  columnname not null

could explains how works?

unique constraint created on column or not ?

to answer first question: when index filtered, doesn't fix criteria in clause left out of index.
if index unique, uniqueness enforced on data fits criteria in clause.

to answer second question: in sql server unique constraints implemented creating unique indexes under hood, there not difference between them. in case uniqueness enforced on index , not directly on table column.


Comments

Post a Comment

Popular posts from this blog

mongodb - Struggling to get ordered results from the last retrieved article, given array of elements to search in -

-
i have collections of objects structure this: { "_id" : objectid("5233a700bc7b9f31580a9de0"), "id" : "3df7ce4cc2586c37607a8266093617da", "published_at" : isodate("2013-09-13t23:59:59z"), ... "topic_id" : [ 284, 9741 ], ... "date" : numberlong("1379116800055") } i'm trying use following query: db.collection.find({"topic_id": { $in: [ 9723, 9953, 9558, 9982, 9833, 301, ... 9356, 9990, 9497, 9724] }, "date": { $gte: 1378944001000, $lte: 1378954799000 }, "_id": { $gt: objectid('523104ddbc7b9f023700193c') }}).sort({ "_id": 1 }).limit(1000) the above query uses topic_id, date index not keep order of returned results. forcing use hint({_id:1}) makes results ordered, nscanned 1 million documents though limit(1000) specified. what missing?
Read more

c# - Pausing a storyboard on TabItem mouse over -

-
i have tab control invisible tabs. when mouse on area of form, calls c# handler runs: ((storyboard)findresource("animate")).begin(hiddentab); the animate storyboard: <storyboard x:key="animate"> <objectanimationusingkeyframes begintime="0:0:0" storyboard.targetproperty="visibility"> <discreteobjectkeyframe keytime="0"> <discreteobjectkeyframe.value> <visibility>visible</visibility> </discreteobjectkeyframe.value> </discreteobjectkeyframe> </objectanimationusingkeyframes> <doubleanimation begintime="0:0:0.0" storyboard.targetproperty="opacity" from="0" to="1" duration="0:0:0.2"/> <doubleanimation begintime="0:0:2.5" storyboard.targetproperty="opacity" from="1" to="0...
Read more

c# - Attribute value in root node of xml Linq to XML -

-
while parsing xml linq xml, came across strange behaviour (atleast me). below first xml parsed `<?xml version="1.0" encoding="utf-8"?> <testrun> <unittestresult testname = "arun" outcome = "i"> </unittestresult> <unittestresult testname = "arun1" outcome = "i"> </unittestresult> </testrun>` my code looks xdocument doc = xdocument.parse(filecontents); var result = doc.descendants("unittestresult"); the above works fine. if root node contain attributes same code not working. reason. xml sample below <?xml version="1.0" encoding="utf-8"?> <testrun id="7903b4ff-8706-4379-b9e8-567034b70abb" name="inaambika@inbelw013312a 2016-02-26 16:55:14" runuser="stc\inaambika" xmlns="http://microsoft.com/schemas/visualstudio/teamtest/2010"> <unittestresult testname = "arun" outcome = "...
Read more