simple que

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simple que

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harri.reddy

Posted Thursday, September 13, 2012 3:39 PM

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hi,

i have 1 table which has millions of rows, i am doing select * from tablename
and select count(*) from tablename

does this both take same time or different,if different then why,if same then why.

(2) If i define variable global variable in my stored proc doesnt it appear inside another stored proc.(nested)

Post #1358915

Eugene Elutin

Posted Thursday, September 13, 2012 4:46 PM

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harri.reddy (9/13/2012)

Looks like interview questions to me.

What are your answers so far?

#2 looks a bit irrelevant to SQL Server Smile

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Post #1358971

GilaMonster

Posted Thursday, September 13, 2012 4:58 PM

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harri.reddy (9/13/2012)

(2) If i define variable global variable in my stored proc doesnt it appear inside another stored proc.(nested)

Perhaps because SQL doesn't have global variables?

For the first, why don't you create such a table, run both queries and see which, if either, is faster?

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1358976

harri.reddy

Posted Thursday, September 13, 2012 5:33 PM

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i dont hv millions of rows ,for simple rows like 100,its time i s 0

Post #1358987

Eugene Elutin

Posted Thursday, September 13, 2012 6:40 PM

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create one!

try this one:

select top 1000000 1 as a
into #t
from sys.columns c1 
cross join sys.columns c2
cross join sys.columns c3
cross join sys.columns c4

_____________________________________________
"The only true wisdom is in knowing you know nothing"
"O skol'ko nam otkrytiy chudnyh prevnosit microsofta duh!" BigGrin

(So many miracle inventions provided by MS to us...)

How to post your question to get the best and quick help

Post #1358997

harri.reddy

Posted Friday, September 14, 2012 6:36 AM

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ok.

select count(*) taking 0 seconds,and select * from taking 0.08

but why?i dont know that

Post #1359220

GilaMonster

Posted Friday, September 14, 2012 6:44 AM

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Have a look at the execution plan.

Also consider, how much data has to be transmitted and displayed in each case?

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1359230

bala.a

Posted Friday, September 14, 2012 7:51 AM

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Literally speaking,

a) "Select *" will return the result set , whereas "Count(*)/Count(1)" will return a scalar value and this will result in significance difference in terms of I/O
b) Other fact is, there is no hard & fast rule to judge the performance; everything depends on the many factors like indexes used, statistics update, etc.....

For your other question, you can pass the variable as a parameter. Do you have any concerns by doing so with respect to your scenario?

Post #1359287

harri.reddy

Posted Friday, September 14, 2012 9:46 AM

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thanks for your response,

for my other question,

it was something ,if i define global variable in sp,will it can be access in inside stored procedure

Post #1359450

bala.a

Posted Friday, September 14, 2012 9:59 AM

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No you can't

Post #1359469

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