For the last query:
select COUNT(convert(int,NULL)) from #temp
It will return 0 because when you execute the query:
SELECT CONVERT(int,NULL) it will return NULL and as the return type of COUNT is INT so NULL will implicitly
converted to '0'.
Hope it will clear to you now Yogi 🙂
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To get quick answer follow this link:
http://www.sqlservercentral.com/articles/Best+Practices/61537/