SQL WHERE IF clause issue - mysql

Question

I have a SQL/Java code issue. The basic overlay is as follows: a MySQL database with a table. In this table there are multiple columns. One column consists of names. An associated column is months. In the third column there is counts. So a sample table would be
john - january - 5
john - january - 6
mary - january - 5
Alex - February- 5
John - February - 6
John - February - 4
Mary - February - 3
John - march - 4
The table continues to month May.
So John appears in five months, Mary in 3, and Alex in one. Currently, my SQL query somewhat looks like this.
select name, sum(count)/4
from table where (category ='something'
AND month not like 'May') group by name;
Basically, what this query is supposed to do is just display each name with the average counts per month. Hence, the sum will be divided by four (because I exclude May, so it must divide Jan-April/4). However, the issue is that some names only appear in one month (or two or three).
This means for that name, the sum of the counts would only be divided by that specific number, to get the average counts over the months. How would I go about this? I feel as if this will require some if statement in a where clause. Kind of like where if the count of the distinct (because months may repeat) is a certain number, then divide the sum(count) by that number for each name?
Also, I think it may not be a where if clause issue. I've read some forums where possibly some use of case could be utilized?

Answer 1

If you need average per month, you can GROUP BY name and month and use AVG function:
SELECT `name`, `month`, avg(`count`)
FROM table
WHERE `category` ='something' AND `month` NOT LIKE 'May'
GROUP BY `name`, `month`;
If you need average for all period, just GROUP BY name and AVG count:
SELECT `name`, avg(`count`)
FROM table
WHERE `category` ='something' AND `month` NOT LIKE 'May'
GROUP BY `name`;
And another option, if you don't like AVG:
SELECT `name`, sum(`count`)/(SELECT count(*) FROM `table` AS `t2` WHERE `category` ='something' AND `month` NOT LIKE 'May' and `t1`.`name` = `t2`.`name`)
FROM `table` AS `t1`
WHERE `category` ='something' AND `month` NOT LIKE 'May')
GROUP BY name;
But I would stay with AVG.
Actually, i prefer to use != instead of NOT LIKE it's improves readability

Answer 2

Just for completness sake here is a WORKING FIDDLE. using the AVG function is the way to go as it will do the average per person per month. look at John in January.. his result is 5.5 when the count (in january) is 5 and 6.. average = 5.5.
SELECT
person,
month,
avg(counter)
FROM testing
where
(
category ='something'
AND month <> 'May'
)
GROUP BY person, month;
If you want to see the data in one like as it sounds like that from your post then you can do this. ANOTHER FIDDLE
SELECT
person,
group_concat(month),
group_concat(average_count)
FROM(
SELECT
person,
month,
avg(counter) as average_count
FROM testing
where
(
category ='something'
AND month <> 'May'
)
GROUP BY person, month
) as t
group by person;

Answer 3

Try this :
SELECT name, SUM(count) / COUNT(DISTINCT month)
FROM table
WHERE month != 'May'
AND category = 'something'
GROUP BY name