99% working behavior from mysql statement needs to be 100% - mysql

Question

I have inherrited a DB that I've been tasked to mine for Data.
There are 2 tables that are loosely associated - atm and dslams.
The atm table contains "remotename", "rst", and "CardNumber" fields that relate to the dslams "hostname" field.
The atm table contains the port information for the dslam cards and the dslams table contains the information about the dslam card itself.
I've been tasked with printing out all the locations (dslams.name) that have a certain type of card (dslams.model="6256") and a count of all the ports on that card that have a certain level of service (atm.speed LIKE "RI_%%09" OR atm.speed LIKE "RI%%1%").
I've crafted the following statement which almost works...
SELECT distinct(dslams.name) AS Remote, Count(atm.speed) AS Customers, dslams.model
FROM dslams
LEFT JOIN atm
ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
GROUP BY dslams.name
HAVING dslams.model="6256"
ORDER BY dslams.name;
This prints out exactly what I need for all but 1 of the locations.
ie.
MariaDB [dsl]> SELECT distinct(dslams.name) AS Remote, Count(atm.speed) AS Customers, dslams.model
-> FROM dslams
-> LEFT JOIN atm
-> ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
-> GROUP BY dslams.name
-> HAVING dslams.model="6256"
-> ORDER BY dslams.name;
+---------+-----------+-------+
| Remote | Customers | model |
+---------+-----------+-------+
| ANTH-C2 | 1 | 6256 |
| BETY-C2 | 1 | 6256 |
| BHOT-C2 | 6 | 6256 |
| BNSH-C2 | 1 | 6256 |
| BUG2-C2 | 1 | 6256 |
| CCRK-C2 | 0 | 6256 |
...
| STLN-C2 | 1 | 6256 |
| SUMR-C2 | 2 | 6256 |
...
| WGRV-C2 | 0 | 6256 |
+---------+-----------+-------+
63 rows in set (0.34 sec)
For some reason there's one location that's not getting counted - STWL-C2.
MariaDB [dsl]> SELECT distinct(name), model FROM dslams WHERE model="6256" order by name;
+---------+-------+
| name | model |
+---------+-------+
| ANTH-C2 | 6256 |
| BETY-C2 | 6256 |
| BHOT-C2 | 6256 |
| BNSH-C2 | 6256 |
| BUG2-C2 | 6256 |
| CCRK-C2 | 6256 |
...
| STWL-C2 | 6256 |
...
| WGRV-C2 | 6256 |
+---------+-------+
64 rows in set (0.00 sec)
There's no difference in the tables between the STWL-C2 location and the other locations so it should print out with a count of 0.
Can anyone help me figure out why that 1 location is being missed?
Any help or direction would be appreciated as I am a rookie SQL programmer trying to understand this as best I can.
Best Regards,
Joe

Answer 1

Don't use HAVING dslams.model = '6256', put that in the WHERE clause. When you use HAVING, it filters after grouping. When you group by name, the result can contain the model from any row in the group, and it won't necessarily choose model = '6256'.
SELECT dslams.name AS Remote, Count(atm.speed) AS Customers, dslams.model
FROM dslams
LEFT JOIN atm
ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
WHERE dslams.model = '6256'
GROUP BY dslams.name
ORDER BY dslams.name;