Difference between sum and count in sql query

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Hello Experts,

I came across this website during my online search for the above question.
http://www.w3resource.com/sql/aggregate-functions/sum-and-count-using-variable.php[^]

The very first statement in the website says,

To get sum of total number of records in 'customer' table, the following SQL statement can be used

Why can't we use select count(*) from Tablename to get the total number of records?
Basically I didn't the difference of this particular example in the url. Can someone help me with this?

Or can someone tell me how different can we write a query for below but it should return same resultset for both the queries

SQL

select icitem,icdsc1,icdsc2, sum(ifqoh) as onhand, sum(ifqcm) as commit from TESTDATA.VINITMB join TESTDATA.VINITEM on ifcomp=1 and ifitem=icitem and ifdel='A'
where icitem like 'VP%' group by icitem, icdsc1, icdsc2
having sum(ifqoh)=0 order by icitem;

Posted 29-Jun-15 3:45am

sudevsu

Updated 29-Jun-15 3:47am

v2

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Afzaal Ahmad Zeeshan 29-Jun-15 10:05am

COUNT would count the records and give you the result, SUM is used to return the SUM of the values in records.

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Andy Lanng · Accepted Answer · 2015-06-29T04:07:00

Solution 1

It's easy:

You can count anything. You can even ensure its distinct like Count(distinct status)

you can only sum a numerical value. sum adds each row together.

If you had a column with 1,1,1,1,2,2, then:

SQL

Count(col) = 6
Count(Distinct col) = 2
Sum(col) = 8

Hope that helps

Andy ^_^

Posted 29-Jun-15 4:07am

Andy Lanng

Comments

sudevsu 29-Jun-15 16:44pm

Thanks