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it does not matter, you can use either.
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<div>
the difference is:<br />
count(*) will include all the rows.<br />
count(x_id) will not include the row with a null x_id.
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the difference is:
count(*) will include all the rows.
count(x_id) will not include the row with a null x_id.

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In fact, I believe, count(*) is converted to count(primary key) when parsing 
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In fact, I believe, count(*) is converted to count(primary key) when parsing

<div>
I looked up some books, there is nothing that says count(*) is converted to count(primary key) ... my teacher said once it does..., but it says that count(primary key)will work a bit faster <br />
<br />
hope this helps
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I looked up some books, there is nothing that says count(*) is converted to count(primary key) ... my teacher said once it does..., but it says that count(primary key)will work a bit faster

hope this helps

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Great. I was just curious! :) &nbsp;Thanks. &nbsp;I'll leave the queries as the are!<br />
<br />

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Great. I was just curious! :)  Thanks.  I'll leave the queries as the are!



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<div class="content wysiwyg-content">
Is it worth it to go and change queries that were written:<br />
select count(*) from x_table <br />
to <br />
select count(x_id) from x_table <br />
<br />
if x_id is the primary key. &nbsp;I'm thinking that it's worth it because the pk will be indexed, making the count faster...but i'm not sure if it's really worth the time. &nbsp;<br />
<br />
Any advice?<br />
I have to be compatible with Oracle and Sql Server 2000...if that makes a difference...
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</div>


Is it worth it to go and change queries that were written:
select count(*) from x_table 
to 
select count(x_id) from x_table 

if x_id is the primary key.  I'm thinking that it's worth it because the pk will be indexed, making the count faster...but i'm not sure if it's really worth the time.  

Any advice?
I have to be compatible with Oracle and Sql Server 2000...if that makes a difference...

Performance question about select count(*) vs select count(x_id)

Databases are organized collections of data, most commonly accessed through management systems including schemas, tables, queries and processes that allow users to enter and manipulate the information or utilize it in other fashions, such as with web applications or for reporting purposes.