Time Comparison of 2 Queries

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1.Select * From Employee

2.Select EmployeeCode,EmployeeName,Address1,Address2,Address3,Image From Employee

From the above 2 queries Which Elapsed time is less. please explain with details.

Table Structure: Employee

Column Name-----Data Type
EmployeeCode-----varchar(15)
EmployeeName-----varchar(40)
Address1---------varchar(30)
Address2---------varchar(30)
Address3---------varchar(30)
Image------------Image

Posted 17-Dec-13 1:32am

pravin2007.cbe

Updated 17-Dec-13 1:43am

v3

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3 solutions

Solution 2

Hi Pravin,

You should have asked google for this.
No problem I did search for you you can find reason here[^] .

By the way Thanks for asking this question.

Hope this helps you a bit.

Regards,
RK

Posted 17-Dec-13 1:45am

♥…ЯҠ…♥

Comments

[no name] 17-Dec-13 8:08am

Also very general answer. Anyway I put a hint in my answer to your solution.

♥…ЯҠ…♥ 17-Dec-13 8:13am

Thanks Idle63...!!!

[no name] 17-Dec-13 8:43am

That is ok. I also learn by the link you posted ;)

♥…ЯҠ…♥ 17-Dec-13 8:44am

;-)

Solution 1

A general answer is not possible, because in case packages size for one record fits -by "accident"- then there will be no difference in query performance.

Anyway I suggest:
a.) Query only the fields you need. Means no SELECT *
b.) The chance that Image decrease the perfromance is "high"
c.) Always use a where. Imagine you have a table with millions of records....

Please note the link by ♥…ЯҠ…♥ in his answer

Posted 17-Dec-13 1:43am

idle63

Updated 17-Dec-13 1:48am

v3

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Maciej Los · Accepted Answer · 2013-12-17T11:24:00

Solution 3

In addition to solution 1 by RK, i would like to provide another useful links:
SQL SERVER – Time Delay While Running T-SQL Query – WAITFOR Introduction[^]
Getting IO and time statistics for SQL Server queries[^]

There are several things to do to increase query performance (time of execution).
7 performance tips for faster SQL queries[^]
Query Performance[^]

Finall conclusion: a query with list of necessary columns is always faster than SELECT *!

Posted 17-Dec-13 11:24am

Maciej Los

Updated 17-Dec-13 19:44pm

v2

Comments

Tom Marvolo Riddle 18-Dec-13 2:32am

Thanks for this link:7 performance tips for faster SQL queries[^]
my 5!

Maciej Los 18-Dec-13 2:33am

You're very welcome and thank you ;)

[no name] 18-Dec-13 8:46am

Finall conclusion: a query with list of necessary columns is always faster than SELECT *!

=> This statement is definitively wrong!

Maciej Los 18-Dec-13 8:48am

Please elaborate...
Have a look at magic word: "necessary"

Maciej Los 18-Dec-13 8:51am

Have you seen article: "7 performance tips"?