Need Help understanding the HAVING clause as it relates to COUNT - mysql

Question

I am starting to learn sql and I am currently getting hung up on the 'having' clause when I use it in conjunction with COUNT. I have done a lot of research and my general understanding is that unlike where it waits to apply until any functions in the query have run.
This lead me to find the rather neat little function that allows me to find the closest locations to a given zip code by latitude and longitude. I started playing with this and used it to tie together three tables. One has a list of zip codes and their latitude longitudes while the other has a list of events and their zip codes and the last has a list of any special requirements for each event. The three event tables are tied to each other through an index. The latitude/longitude table is tied in via the zip code.
So for example:
SELECT `EVENT_CAT`,
`NAME`,
(3959 * acos(cos(radians(44.643418)) * cos(radians(`Latitude`)) * cos(radians(`Longitude`) - radians(-73.121685) ) + sin( radians(44.643418)) * sin(radians( `Latitude`)))) AS distance
FROM DATA_ZipCodes
JOIN `EVENT_POST_General` ON ZIP_CODE = ZipCode
JOIN `DATA_EVENTCategories` ON EVENT_CAT = DATA_EVENTCategories.ID
JOIN `EVENT_POST_Filtering` ON EVENT_POST_General.EVENT_ID = EVENT_POST_Filtering.EVENT_ID
WHERE `REQUIRE_TICKET` = '0'
HAVING distance < 10
ORDER BY distance
This works great and returns:
EVENT_CAT NAME DISTANCE
-------------------------------
1 CONCERT 1
1 CONCERT 1
1 CONCERT 1
2 GAMES 1
2 GAMES 2
3 DANCE 4
4 DINNER 4
5 MOVIES 4
The catch is I also want to be able to just query a count of how many of each category of events I have.
To this end I tried just encorporating a COUNT and GROUP BY
SELECT COUNT(`EVENT_CAT`),
`NAME`,
(3959 * acos(cos(radians(44.643418)) * cos(radians(`Latitude`)) * cos(radians(`Longitude`) - radians(-73.121685) ) + sin( radians(44.643418)) * sin(radians( `Latitude`)))) AS distance
FROM DATA_ZipCodes
JOIN `EVENT_POST_General` ON ZIP_CODE = ZipCode
JOIN `DATA_EVENTCategories` ON EVENT_CAT = DATA_EVENTCategories.ID
JOIN `EVENT_POST_Filtering` ON EVENT_POST_General.EVENT_ID = EVENT_POST_Filtering.EVENT_ID
WHERE `REQUIRE_TICKET` = '0'
GROUP BY `EVENT_CAT`
HAVING distance < 10
ORDER BY distance
When I do this however the response does not error but it also does not return anything. I am very baffled as to how to best do this. I tried moving the group by but that just caused errors.
*EDITED TO CORRECT THE GROUP_BY TO GROUP BY as that was a type when I was pasting it in here and is not in the original code :)

Answer 1

Your query a bit shorted:
SELECT COUNT(`EVENT_CAT`),`NAME`, ... as `distance`
FROM ...
WHERE `REQUIRE_TICKET` = '0'
GROUP_BY `EVENT_CAT`
HAVING distance < 10
ORDER BY distance
The group by clause (I think it should not have a _ there, too) groups the result by different event_cat results, unifying the rest of the results. But:
your query result does not even contain such a column.
in each group you try to count how much different values of event_cat there are. There can only be one, if you would group by this.
additionally, the other columns of the result are not depending only on the group-by column ... this does not work.
The having clause is used to filter the resulting groups after grouping. Since your distance is not unique in each group, this is not a good way to do it - put it instead in the WHERE clause, if you want to count how many events in 10 km distance are in each category. The problem is that you can't refer in the WHERE clause to fields only defined in the SELECT clause, so we need to put the formula into the WHERE clause.
Then count the different name values (or something else unique), not the event_cat.
SELECT `EVENT_CAT`, COUNT(`NAME`)
FROM ...
WHERE `REQUIRE_TICKET` = '0' AND ... < 10
GROUP_BY `EVENT_CAT`
Ordering by distance also is not possible, since the distance is not unique by category. Maybe ordering by count, or minimal distance, or such?

Answer 2

Use:
SELECT dzc.name,
COUNT(dzc.name),
(3959 * acos(cos(radians(44.643418)) * cos(radians(`Latitude`)) * cos(radians(`Longitude`) - radians(-73.121685) ) + sin( radians(44.643418)) * sin(radians( `Latitude`)))) AS distance
FROM DATA_ZipCodes dzc
JOIN EVENT_POST_General epg ON epg.zip_code = dzc.zipcode
JOIN DATA_EVENTCategories dec ON dec.id = dzc.event_cat
JOIN EVENT_POST_Filtering epf ON epf.event_id = epg.event_id
WHERE REQUIRE_TICKET = '0'
GROUP BY dzc.name
HAVING distance < 10
ORDER BY distance
you had a typo - there's no underscore in "GROUP BY"
MySQL supports hidden columns in the GROUP BY, but few other databases do
You only need backticks in MySQL queries if you are escaping reserved/key words
use table aliases -- makes the query more readable, and will give you more specific errors in the event a table gets changed