How to create a mysql trigger to update a column - mysql

Question

I want to update a column of new inserted row based on value set in another table.
I have created some thing like this :
BEGIN
DECLARE value float;
DECLARE comission float;
DECLARE c float;
select value=`uc_amount` from inserted;
select comission=`config_value` from fixed_configs WHERE `config_key` = 'deal_comission';
c = value - (value * (comission/100));
update user_credits set `uc_admin_amount`=value;
END
But its shows error
here table structure
user_credit:
uc_amount float(10,2)
uc_admin_amount float(5,2)
uc_created timestamp
uc_extra text
fixed_configs:
config_key varchar(225)
config_value varchar(225)

Answer 1

You basically need 2 triggers one before insert and one before update
The before insert will get the uc_amount and will calculate the uc_admin_amount and before update will check if the old uc_amount is not same as new uc_amount and if so do the calculation.
delimiter //
create trigger ins_user_credit before insert on user_credit
for each row
begin
declare comission float(5,2);
select config_value into comission from fixed_configs WHERE config_key = 'deal_comission';
set new.uc_admin_amount = new.uc_amount - (new.uc_amount * (comission/100));
end; //
delimiter ;
delimiter //
create trigger upd_user_credit before update on user_credit
for each row
begin
declare comission float(5,2);
if(old.uc_amount <> new.uc_amount)
select config_value into comission from fixed_configs WHERE config_key = 'deal_comission';
set new.uc_admin_amount = new.uc_amount - (new.uc_amount * (comission/100));
end if ;
end; //
delimiter ;