How to use the Having Clause

[SchweppesAle]

Hi, I've used the following query to check for any duplicate email addresses in our table.  The problem is, I'm not entirely sure what the difference is between both the having and where clauses so I was hoping someone could confirm whether this would work or not.

 

 

SELECT COUNT(id) AS Quantity 
FROM huge_email_list 
GROUP BY email 
HAVING ( COUNT(email) = 1 )

 

My concern is that the query will eliminate email addresses which have multiple entries from the total sum(Quantity) entirely rather than counting them as an additional 1 entry. 

 

Is this where the Having clause comes into play? 

[SchweppesAle]

Alright, this clearly wasn't working

 

Thinking that I might just need to include the GROUP BY email clause in order to count the unique email addresses

 

Still, I was hoping someone could clarify the difference between WHERE and HAVING; I really can't tell the difference. 

[Mchl]

HAVING is almost like WHERE. The difference is, you can use functions and statements in having clause, while you can not in where.

 

Also WHERE coonditions are applied before HAVING conditions.

[SchweppesAle]

HAVING is almost like WHERE. The difference is, you can use functions and statements in having clause, while you can not in where.

 

Also WHERE coonditions are applied before HAVING conditions.

 

Thanks for clearing that up

[Mchl]

There are in fact further differences, but those are essential I think.