MySQL Trigger statement fails with variable assignment - mysql

Question

Following is the definition for Patients table:
Patients table Columns:
PatientId int AI PK
FirstName longtext
LastName longtext
Email longtext
NIC longtext
Phone longtext
Address longtext
City longtext
Country longtext
DOB datetime(6)
Gender longtext
Reference longtext
SerialNumberYear smallint
SerialNumber int
DoctorId int
CreatedOn datetime(6)
UpdatedOn datetime(6)
CreatedBy longtext
SMS_Allowed tinyint(1)
Email_Allowed tinyint(1)
SpecialConcern1 longtext
SpecialConcern2 longtext
SpecialConcern3 longtext
SpecialConcern4 longtext
CustomYearlyId longtext
YearlyId int
I have the following trigger in MySQL on this table:
CREATE TRIGGER generate_yearly_id BEFORE INSERT ON clinic.patients
FOR EACH ROW
BEGIN
DECLARE last_id INTEGER default 10;
DECLARE current_year DATE;
DECLARE yearly_id INTEGER default 0;
IF NEW.CustomYearlyId IS NULL THEN
BEGIN
INSERT INTO DEBUG VALUES (null,"start trigger");
#SET #last_id := (SELECT max(yearlyid) FROM patients WHERE
# YEAR(createdon)=YEAR(CURDATE()));
IF last_id IS NOT NULL THEN
BEGIN
SET #yearly_id = 1;
INSERT INTO DEBUG VALUES (null, concat("in if lastid is not null ",#yearly_id));
END;
ELSE
BEGIN
#SET #yearly_id := 1;
END;
END IF;
SET NEW.yearlyid := #yearly_id;
END;
END IF;
END;//
delimiter ;
The statement SET #yearly_id = 1; works fine. But if I change it to SET #yearly_id = #last_id;, the trigger fails. What am I doing wrong in making this assignment? last_id has a default value, so do I need to initialize it?

Answer 1

The following code works perfectly. Differences are 1. Variables have been initialized before being used. Apparently default value is not enough. 1. Count has been used in the "if" condition instead of testing for "is null".
CREATE TRIGGER generate_yearly_id BEFORE INSERT ON clinic.patients
FOR EACH ROW
BEGIN
DECLARE last_id INTEGER default 0;
DECLARE current_year DATE;
DECLARE yearly_id INTEGER default 1;
declare count INTEGER default 0;
IF NEW.CustomYearlyId IS NULL THEN
BEGIN
#init last_id to some value before using
SET #last_id = 0;
SET #yearly_id = 0;
#INSERT INTO DEBUG VALUES (null,"start trigger");
set #count := (select count(*) from patients where
YEAR(CreatedOn)=YEAR(curdate()));
IF #count > 0 THEN
BEGIN
SET #last_id := (SELECT max(yearlyid) FROM patients WHERE
YEAR(createdon)=YEAR(CURDATE()));
SET #yearly_id = #last_id + 1;
SET NEW.yearlyid := #yearly_id;
#INSERT INTO DEBUG VALUES (null, concat("in if lastid is not null ",#yearly_id));
END;
ELSE
BEGIN
#INSERT INTO DEBUG VALUES (null, concat("in else ",#yearly_id));
#SET #yearly_id = 1;
SET NEW.yearlyid := 1;
END;
END IF;
#Set NEW.yearlyid := 1;
END;
END IF;
END;//
delimiter ;