SQL Count

The SQL Count is an important function that I use when I am exploring a new table.

I often use it to see how big a table is, but I also use it to determine counts within a group.

Let’s take a look at it’s uses.

Here is the employee table:

select * 
from employee; 

Results:

You can tell this has 14 records, but imagine that it had 1,000,000 records.

You wouldn’t be able to just select * without it taking a while to bring all of the records back.

That is where the SQL Count comes in:

select count(*) 
from employee; 

Here you can see it gave us one column with the count of the whole table.

Pretty simple.

Now, what if we wanted to find out how many people had a commission?

If we look above, we can simply count those people.  But, we have this new SQL Count function.

So, let’s use it:

select count(commision) 
from employee; 

Will we get 14 records, or 4 records?

Well, here are the results:

We only got 4 records.  Why is that?…

That is because the count function doesn’t count NULL records.  Again, if you look above, you will see a bunch of commissions that have the value of NULL.

This NULL value means we don’t have a value.  So, when the SQL Count  function looks at those rows, it ignores them.

But, look at the 10th row above.  It has a “0.00” value.  Why does it count that one?

Because, even though the value is 0, it is still a value (it isn’t null).

An that’s it.  That’s how you use the SQL Count function.