Why using "Select field1,field2... from table " is better performance than "Select * from table "?

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Why using "Select EmployeeId,EmployeeName from empTable" is better performance than "Select * from empTable"?

Let assume that in empTable there is two field EmployeeId and EmployeeName
if we want to retrieve all the records then we may use the following command
Select * from empTable;
but the better performance ...if we use
Select EmployeeId,EmployeeName from empTable;command.

please tell me why?

Posted 2-Jul-13 20:08pm

Tanumay99

Updated 2-Jul-13 20:18pm

Kuthuparakkal

v4

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Thanks7872 · Answer 1 · 2013-07-02T20:16:00

Solution 1

Refer to this link

Top Ten SQL Performance Tips[^][Refer to tip3 and tip4]

SQL Tuning or SQL Optimization[^]

:doh:[Edit]:

Efficient SELECT statements[^]

Regards.. :laugh:

Posted 2-Jul-13 20:16pm

Thanks7872

Updated 2-Jul-13 20:17pm

v2

Comments

Tanumay99 3-Jul-13 2:21am

I know this is use for SQL-Server optimization process. and I read related information regarding that.But i donot understand how it optimize...?
please share if you konw how it works...

Thanks7872 3-Jul-13 2:23am

You have not refered to any of the link above.If you did,then you would get the answer.Explaination is there.

Tanumay99 4-Jul-13 1:08am

thanks for your help

Thanks7872 4-Jul-13 1:09am

You are welcome.Call again.

srinvias kumar lumeris · Answer 2 · 2013-07-02T20:23:00

Solution 2

i think, in this scenario no change in performance

but in cases

table have 10 columns but you need 3 columns only, in that this improves performance

* - which will return all columns in the table -> degrades performance

specified - will returns specified columns only -> improves performance

Posted 2-Jul-13 20:23pm

srinvias kumar lumeris

Comments

Tanumay99 3-Jul-13 2:40am

my questen is...
if there is 10 columns and if we use "select *" command to retrieve all the fields and if we use
"select field1,.....field10" to retrieve all the fields....then second one is better to performance .
my questn is why??
please try to understand my questn...