Before insert trigger prevents following INSERT INTO statements to execute - mysql

Question

I have a problem with the following sql code executed in MySQL Workbench 5.6. The table is orderly created, the trigger creation code is also run without errors. But when I try to run the both insert into statements I have an error Error Code: 1054. Unknown column 'Pass' in 'field list'. If I run the last select statements it is also runned as expected!?
I really can not imagine what is happening after running the trigger creation script!?
If I do not run the triger creation code before the insert into statements they are executed as expected and the data is inserted in the columns.
/*TASK 15: Write a SQL statement to create a table Users. Users should have username,
password, full name and last login time. Choose appropriate data types for the table fields.
Define a primary key column with a primary key constraint. Define the primary key column
as identity to facilitate inserting records. Define unique constraint to avoid repeating
usernames. Define a check constraint to ensure the password is at least 5 characters long.
*/
create table Users(
UserID int auto_increment not null,
Username nvarchar(50) not null,
Pass varchar(100) not null,
FullName nvarchar(100),
LastLoginTime datetime,
constraint PK_Users primary key(UserID),
constraint UK_Users_Username UNIQUE(Username),
constraint CH_Users_Password CHECK(length(users.Pass)>=5)
);
DELIMITER $$
CREATE TRIGGER `TR_BeforeInsert_Users`
BEFORE INSERT ON `users`
FOR EACH ROW
BEGIN
IF LENGTH(`Pass` ) < 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint on Pass failed';
END IF;
END$$
delimiter ;
Insert into Users(Username, Pass, FullName,lastlogintime) values('ttitto','alabala','Todor', now());
Insert into Users(Username, Pass, FullName,lastlogintime) values('ttitt','ala','Todor', now());
select length(Pass) from users;

Answer 1

Within triggers, one must reference columns with either the NEW or OLD pseudo-table prefix. In your case:
DELIMITER $$
CREATE TRIGGER `TR_BeforeInsert_Users`
BEFORE INSERT ON `users`
FOR EACH ROW
BEGIN
IF CHAR_LENGTH(NEW.Pass) < 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint on Pass failed';
END IF;
END$$
delimiter ;