SQL HAVING Tutorial

Use SQL HAVING to filter summary results from a GROUP BY.  It specifies the search condition for the group or aggregate.

SQL HAVING is only used with SELECT.  It is mostly used when a GROUP BY is present, if one isn’t there is an implicit single aggregated group.

When constructing a SELECT statement using HAVING the order is:

SELECT columnlist
FROM table
WHERE condition
GROUP BY columns
HAVING condition
ORDER by column list.

So what do we mean that SQL HAVING filters summary results?  Let’s look at an example:

SQL HAVING Example

Consider the following query which returns the per year pro baseball team batting statistics:

-- Answer
SELECT yearID
	 , teamID
	 , SUM(ab) AS [At Bats]
	 , SUM(hr) AS [Home Runs]
FROM Batting
GROUP BY yearid
	   , teamid
ORDER BY yearid
	   , teamid;

How do we filter the results?  If we use WHERE, we’ll end up filtering rows before they’re summarized. 

Keep in mind it is easy to get WHERE and HAVING mixed up.  They are not the same and serve completely different purposes!

To filer the summarized rows we’ll use SQL HAVING.  Let’s only show batting stats for teams 250 or more home runs within a season!

-- Answer
SELECT yearID, 
       teamID, 
       SUM(ab) AS [At Bats], 
       SUM(hr) AS [Home Runs]
FROM Batting
GROUP BY yearid, 
         teamid
HAVING Sum(hr) > 250
ORDER BY yearid, 
         teamid;

HAVING Clause Expressions

You can also do calculation with the aggregate function with the SQL HAVING.  In this example we’re returning all batting seasons where 4.5% of the at bats results in home runs:

-- Answer
SELECT yearID, 
       teamID, 
       SUM(ab) AS [At Bats], 
       SUM(hr) AS [Home Runs]
FROM Batting
GROUP BY yearid, 
         teamid
HAVING (CAST(Sum(hr) as float) / CAST(Sum(ab) as float)) >= 0.045
ORDER BY yearid, 
         teamid;

Notice I had to use CAST to convert the data type.

Now why don’t you try one. Can you write a query in the space below to count the number of “At Bats” and “Home Runs” by year? Only include years where the “At Bats” were greater than 100,000?

/*  Answer */
SELECT yearID,  
       SUM(ab) AS [At Bats], 
       SUM(hr) AS [Home Runs]
FROM Batting
GROUP BY yearid 
HAVING SUM(ab) > 100000
ORDER BY yearid

Additional Resources

If you’re looking to learn more about using the HAVING clause, then I would recommend these resources:

• What is the Difference between Where and Having Clauses?
• SQL GROUP BY Guide