Count on multiple tables with missing zero counts - mysql

Question

I am running this query to return data with count < 0. It works fine until count is > 0 and < 50. But when count becomes 0, it doesnot return the data. Count is defined by coupons`.`status. On count zero, there will be no data in coupons table with status as 1. This is creating the issue, as it omits the whole row.
SELECT count(*) AS count, clients.title, plans.name
FROM `coupons`
INNER JOIN `clients` ON `coupons`.`client_id` = `clients`.`id`
INNER JOIN `plans` ON `coupons`.`plan_id` = `plans`.`id`
WHERE `coupons`.`status` = 1
GROUP BY `coupons`.`client_id`, `coupons`.`plan_id`
HAVING count < 50
Please help how to fix it.
Table definitions.
coupons (id, client_id, plan_id, customer_id, status, code)
plans (id, name)
clients (id, name...)
client_plans (id, client_id, plan_id)
Basically, a client can have multiple plans and a plan can belong to multiple clients.
Coupons table stores predefined coupons which can be allocated to customers. Non allocated coupons have status as 0, while as allocated coupons get status as 1
Here I am trying to fetch non allocated client wise, plan wise coupon count where either the count is less than 50 or count has reached 0
For example,
If coupons table as 10 rows of client_id = 1 & plan_id = 1 with status as 1, it should return count as 10, but when the table has 0 rows with client_id = 1 and plan_id = 1 with status as 1, it does not return anything in the above query.

Answer 1

Thank you all for your inputs, this worked.
select
sum(CASE WHEN `coupons`.`status` = 1 THEN 1 ELSE 0 END) as count,
clients.title,
plans.name
from
`clients`
left join
`coupons`
on
`coupons`.`client_id` = `clients`.`id`
left join
`plans`
on
`coupons`.`plan_id` = `plans`.`id`
group by
`coupons`.`client_id`,
`coupons`.`plan_id`
having
count < 50

Answer 2

With the inner joins, the query is not going to return any "zero" counts.
If you want to return "zero" counts, you are going to need an outer join somewhere.
But it's not clear what you are actually trying to count.
Assuming that what you are trying to get is a count of rows from coupons, for every possible combination of rows from plans and clients, you could do something like this:
SELECT COUNT(`coupons`.`client_id`) AS `count`
, clients.title
, plans.name
FROM `plans`
CROSS
JOIN `clients`
LEFT
JOIN `coupons`
ON `coupons`.`client_id` = `clients`.`id`
AND `coupons`.`plan_id` = `plans`.`id`
AND `coupons`.`status` = 1
GROUP
BY `clients`.`id`
, `plans`.`id`
HAVING `count` < 50
This is just a guess at result set you are expecting to return. Absent table definitions, example data, and the expected result, we're just guessing.
FOLLOWUP
Based on your comment, it sounds like you want conditional aggregation.
To "count" only the rows in coupons that have status=1, you can do something like this:
SELECT SUM( `coupons`.`status` = 1 ) AS `count`
, clients.title
, plans.name
FROM `coupons`
JOIN `plans`
ON `plans`.`id` = `coupons`.`plan_id`
JOIN `clients`
ON `clients`.`id` = `coupons`.`client_id`
GROUP
BY `clients`.`id`
, `plans`.`id`
HAVING `count` < 50
There are other expressions you can use to get the conditional "count". For example
SELECT COUNT( IF(`coupons`.`status`=1, 1, NULL) ) AS `count`
or
SELECT SUM( IF(`coupons`.`status`=1, 1, 0) ) AS `count`
or, for a more ANSI standards compatible approach
SELECT SUM( CASE WHEN `coupons`.`status` = 1 THEN 1 ELSE 0 END ) AS `count`