sum(amount) from three tables returning null - mysql

Question

I am having following tables
create table supplier_paid_details(
id bigint(10) NOT NULL AUTO_INCREMENT,
payment_mode varchar(20),
payment_date date,
add_date timestamp DEFAULT 0,
status varchar(20),
supp_payment_id bigint(10) NOT NULL,
primary Key(id),
CONSTRAINT fk_paid FOREIGN KEY (supp_payment_id)
REFERENCES supplier_payment_details(id)
);
create table supplier_paid_check(
id bigint(10) NOT NULL AUTO_INCREMENT,
check_no bigint(10) NOT NULL,
dated date,
payable_at varchar(50),
paid_to_acc_no varchar(30),
paid_to_bank varchar(30),
paid_to_branch varchar(30),
spd_id bigint(10),
add_date timestamp DEFAULT 0,
amount float(10,2),
status varchar(20),
primary Key(id),
CONSTRAINT fk_ckeck FOREIGN KEY (spd_id)
REFERENCES supplier_payment_details(id)
);
create table supplier_paid_online(
id bigint(10) NOT NULL AUTO_INCREMENT,
pay_ref_no varchar(50),
paid_from_bank varchar(50),
from_acc_no varchar(50),
paid_to_acc_no varchar(30),
paid_to_bank varchar(30),
paid_to_branch varchar(30),
spd_id bigint(10),
add_date timestamp DEFAULT 0,
amount float(10,2),
status varchar(20),
primary Key(id),
CONSTRAINT fk_online FOREIGN KEY (spd_id)
REFERENCES supplier_paid_details(id)
);
create table supplier_paid_cash(
id bigint(10) NOT NULL AUTO_INCREMENT,
to_person varchar(40),
designation varchar(40),
receipt_no varchar(30),
spd_id bigint(10),
add_date timestamp DEFAULT 0,
amount float(10,2),
status varchar(20),
primary Key(id),
CONSTRAINT fk_cash FOREIGN KEY (spd_id)
REFERENCES supplier_paid_details(id)
);
Here I would like to sum amounts from supplier_paid_check,supplier_paid_cash,supplier_paid_online.
for that I am using following query but this is showing null.
select sum(ca.amount+ch.amount+onl.amount) as amount from
supplier_paid_details as pd
left join supplier_paid_cash as ca
on pd.id=ca.spd_id
left join supplier_paid_check as ch
on pd.id=ch.spd_id
left join supplier_paid_online as onl
on pd.id=onl.spd_id
where pd.supp_payment_id=1;

Answer 1

I suppose there is at least one row in one of your three tables where amount has a NULL value. This leads to NULL as result in the end as the DBMS could not determine how to handle this value in combination with the other. But there is a way out: you could tell your DBMS what to do with NULL values. Use IFNULL.
select
sum(IFNULL(ca.amount, 0) + IFNULL(ch.amount, 0) + IFNULL(onl.amount, 0)) as amount
from
supplier_paid_details as pd left join supplier_paid_cash as ca on pd.id=ca.spd_id
left join supplier_paid_check as ch on pd.id=ch.spd_id
left join supplier_paid_online as onl on pd.id=onl.spd_id
where
pd.supp_payment_id=1;
Read more on IFNULL at MySQL Docs.

Answer 2

Try this:
select sum(
coalesce(ca.amount, 0)
+ coalesce(ch.amount, 0)
+ coalesce(onl.amount, 0)
) as amount from
....
or this:
select sum(ca.amount) + sum(ch.amount) + sum(onl.amount) as amount from
....