Change MySQL query from WHERE to LEFT JOIN - mysql

Question

I have a query which reports on Asterisk call usage and queue statistics. The query currently uses MySQL WHERE clauses to join the tables and filter the data.
This is how the query looks at present:
SELECT
c.name as 'Agent',
e.extended_number AS 'Extension',
COUNT(ql.`time`) AS 'Total Inbound Calls',
(SELECT
COUNT(1)
FROM
call_history ch,
ast_queue_mstatus qm
WHERE
ch.start >= (DATE_SUB(DATE(NOW()),
INTERVAL 10050 MINUTE))
AND ch.start <= (DATE(NOW()))
AND ch.calltype = 'out'
AND ch.flow = 'out'
AND ch.extension_number = qm.membername
AND qm.membername = e.extended_number
GROUP BY qm.membername) AS 'Total Outbound Calls',
FORMAT(SUM(CAST(ql.arg2 AS UNSIGNED)) / 60, 2) AS 'Total Inbound Duration',
FORMAT(AVG(CAST(ql.arg2 AS UNSIGNED)) / 60, 2) AS 'Avg Inbound Duration',
FORMAT(AVG(CAST(ql.arg1 AS UNSIGNED)) / 60, 2) AS 'Avg Caller Hold Time'
FROM
ast_queue_log ql,
ast_queue_mstatus qs,
client c,
extension e
WHERE
ql.queuename = '1234'
AND ql.`time` >= (DATE_SUB(DATE(NOW()), INTERVAL 7 DAY))
AND ql.`time` <= (DATE(NOW()))
AND (ql.event = 'COMPLETEAGENT'
OR ql.event = 'COMPLETECALLER'
OR ql.event = 'COMPLETETRANSFER')
AND RIGHT(ql.agent, 8) = qs.membername
AND qs.membername = e.extended_number
AND e.client_id = c.id
GROUP BY ql.agent
ORDER BY c.name;
The problem that I have is that I need to return outbound call results for queue members that have not received any inbound calls. At the moment if there are no records in ast_queue_log then the WHERE clause excludes the records, which means they do not get picked up by the scalar sub query.
How can I change this query so I get all call records from call_history where there is a corresponding record in ast_queue_mstatus?
Sorry if this is too complex or there is not enough info, I can try to simplify if this makes no sense!

Answer 1

It's time to ditch those old comma separated list of tables and use the join standard that was introduced in 1992 (yes). :-)
Because then you can use a LEFT JOIN. With this kind of join, the relationship is optional. That is, all rows in the first table are returned (if they match the conditions in the WHERE clause), but the joined table doesn't have to have records as well.
If it doesn't, a row is still returned, but the fields are filled with NULL value.
SELECT
c.name as 'Agent',
e.extended_number AS 'Extension',
COUNT(ql.`time`) AS 'Total Inbound Calls',
(SELECT
COUNT(1)
FROM
call_history ch
INNER JOIN ast_queue_mstatus qm
ON qm.membername = ch.extension_number
WHERE
ch.start >= (DATE_SUB(DATE(NOW()), INTERVAL 10050 MINUTE))
AND ch.start <= (DATE(NOW()))
AND ch.calltype = 'out'
AND ch.flow = 'out'
AND ch.extension_number = e.extended_number
GROUP BY
ch.extension_number) AS 'Total Outbound Calls',
FORMAT(SUM(CAST(ql.arg2 AS UNSIGNED)) / 60, 2) AS 'Total Inbound Duration',
FORMAT(AVG(CAST(ql.arg2 AS UNSIGNED)) / 60, 2) AS 'Avg Inbound Duration',
FORMAT(AVG(CAST(ql.arg1 AS UNSIGNED)) / 60, 2) AS 'Avg Caller Hold Time'
FROM
client c,
INNER JOIN extension e
ON e.client_id = c.id
INNER JOIN ast_queue_mstatus qs
ON qs.membername = e.extended_number
LEFT JOIN ast_queue_log ql
ON ql.queuename = '1234'
AND ql.`time` >= (DATE_SUB(DATE(NOW()), INTERVAL 7 DAY))
AND ql.`time` <= (DATE(NOW()))
AND (
ql.event = 'COMPLETEAGENT'
OR ql.event = 'COMPLETECALLER'
OR ql.event = 'COMPLETETRANSFER')
AND RIGHT(ql.agent, 8) = qs.membername
GROUP BY ql.agent
ORDER BY c.name;
You can use RIGHT JOIN as well to join the other way around (first table is optional). But in general this is harder to interpret.