Parentheses in mysql query giving different results - mysql

Question

I have a query that is giving me different results when i enclosed it in Parentheses, however when I run it without Parentheses its giving me different results. I want to apply Union in between so I have to use Parentheses as without union doesn't work.
The query is as follows:
SELECT Distinct
recurring_billing.id,
recurring_billing.kid_id,
recurring_billing.class_id,
recurring_billing.app_id,
recurring_billing.Region_ID,
CC.month_name,
CC.billing_year,
CASE
WHEN
CC.month_name = recurring_billing.billing_month
AND CC.billing_year = recurring_billing.billing_year
THEN
recurring_billing.billing_status
ELSE
'Pending'
END
AS billing_status, tblkids.kid_name, tblkids.kid_Lastname, tblkids.kid_EMail, tbl_app.app_CCExp AS cc_exp, tbl_app.app_CCName AS cc_name, tbl_app.app_CCNumber AS cc_number, tbl_app.app_CCType AS cc_type, tblclasses.cla_EndDate, tblclassdays.classday_day, CC.remainingclasses, tbl_app.cost_per_class, CC.remainingclasses * tbl_app.cost_per_class AS cost_amount,
CASE
WHEN
OP.override_amt IS NOT NULL
THEN
OP.override_amt
ELSE
CC.remainingclasses * tbl_app.cost_per_class
END
AS pmt_amount,
CASE
WHEN
OP.process_payment = False
THEN
OP.process_payment
ELSE
True
END
AS process_payment
FROM
recurring_billing
LEFT JOIN
tblkidsxclass
ON recurring_billing.kid_id = tblkidsxclass.kxc_kidid
AND recurring_billing.app_id = tblkidsxclass.kxc_appid
LEFT JOIN
tbl_app
ON recurring_billing.app_ID = tbl_app.app_ID
LEFT JOIN
tblkids
ON recurring_billing.kid_id = tblkids.kid_ID
LEFT JOIN
tblclasses
ON recurring_billing.class_id = tblclasses.cla_ID
LEFT JOIN
tblclassdays
ON tblclasses.cla_ID = tblclassdays.classday_classID
INNER JOIN
(
SELECT
MONTHNAME(classday_day) AS month_name,
YEAR(classday_day) AS billing_year,
cla_ID,
COUNT(classday_classid) AS remainingclasses,
c.cost_per_class AS cost_per_class,
COUNT(classday_classid) * cost_per_class AS TotalClassCost
FROM
tblclassdays
JOIN
(
SELECT
tblclasses.cla_ID,
tblclasses.cost_per_class,
tblclasses.cla_nextclass AS next1,
tblclasses_1.cla_nextclass AS next2
FROM
tblclasses
LEFT JOIN
tblclasses AS tblclasses_1
ON tblclasses.cla_nextclass = tblclasses_1.cla_ID
WHERE
tblclasses.cla_ID IN
(
SELECT DISTINCT
recurring_billing.class_id
FROM
recurring_billing
LEFT JOIN
tblkidsxclass
ON recurring_billing.kid_id = tblkidsxclass.kxc_kidid
AND recurring_billing.app_id = tblkidsxclass.kxc_appid -- LEFT JOIN tblkids ON recurring_billing.kid_id = tblkids.kid_ID
LEFT JOIN
tblclasses
ON recurring_billing.class_id = tblclasses.cla_ID -- LEFT JOIN tblclassdays ON tblclasses.cla_ID = tblclassdays.classday_classID
WHERE
ISNULL(tblkidsxclass.kxc_dropoutdate)
AND tblkidsxclass.pmt_option = 'Recurring'
AND tblclasses.cla_active = TRUE -- AND tblclasses.cla_EndDate >= NOW()
GROUP BY
recurring_billing.id
)
)
c
ON tblclassdays.classday_classid IN
(
c.cla_ID,
c.next1,
c.next2
)
WHERE
tblclassdays.classday_noclass = FALSE
AND MONTH(classday_day) = 11
AND YEAR(classday_day) = 2020
AND
(
CONCAT(CAST(classday_day AS DATE), ' ', CAST(classday_endtime AS TIME)) > CAST(CURDATE() AS DATETIME)
)
GROUP BY
cla_ID
)
CC
ON CC.cla_ID = tblclassdays.classday_classID
LEFT JOIN
override_payments OP
ON recurring_billing.app_id = OP.app_id
AND recurring_billing.kid_id = OP.kid_id
AND CC.month_name = OP.billing_month
AND CC.billing_year = OP.billing_year
WHERE
ISNULL(tblkidsxclass.kxc_dropoutdate)
AND tblkidsxclass.pmt_option = 'Recurring'
AND tblclasses.cla_active = TRUE
AND recurring_billing.kid_id NOT IN
(
SELECT
kid_id
from
recurring_billing
where
billing_month = 'November'
and billing_year = '2020'
)
-- AND tblclasses.cla_EndDate >= NOW()
GROUP BY
recurring_billing.id
ORDER BY
recurring_billing.id ASC
Same query if enclosed in Parentheses will give me different results.

Answer 1

Parentheses are not required for a UNION statement. The following 2 union statements both work and yield the same results.
SELECT 1 UNION SELECT 2;
(SELECT 1) UNION (SELECT 2);