InnoDB MySql Error 1215无法添加外键约束，即使在删除DELETE的级联义务之后也是如此

Question

I'm trying to add foreign keys to my two tables Problem and File. These are the CREATE queries. And both tables are created successfully:

CREATE TABLE lpsolve.tbl_file (
  id INT(11) NOT NULL AUTO_INCREMENT,
  problem_id INT(11) DEFAULT NULL,
  title VARCHAR(255) DEFAULT NULL,
  description VARCHAR(255) DEFAULT NULL,
  type VARCHAR(255) DEFAULT NULL,
  create_time DATETIME DEFAULT NULL,
  PRIMARY KEY (id)
)
ENGINE = INNODB
AUTO_INCREMENT = 1
CHARACTER SET latin1
COLLATE latin1_swedish_ci;

CREATE TABLE lpsolve.tbl_probem (
  id INT(11) NOT NULL AUTO_INCREMENT,
  title VARCHAR(255) DEFAULT NULL,
  description VARCHAR(255) DEFAULT NULL,
  create_time DATETIME DEFAULT NULL,
  number_of_files INT(11) DEFAULT NULL,
  PRIMARY KEY (id)
)
ENGINE = INNODB
AUTO_INCREMENT = 1
CHARACTER SET latin1
COLLATE latin1_swedish_ci;

But when I try to add the following constraint I get the Error 1215 Error. This is the add constraint query:

ALTER TABLE tbl_file
ADD CONSTRAINT fk_problem_file
FOREIGN KEY (problem_id)
REFERENCES tbl_problem(id) 
ON DELETE CASCADE
ON UPDATE RESTRICT

The query does not work even by removing the ON DELETE CASCADE and ON UPDATE RESTRICT either. There are a couple of similar problems mentioned in Stack Overflow but they did not answer my problem unfortunately.

Error message:

Cannot add foreign key constraint

Answer 1

The table name is tbl_probem

CREATE TABLE lpsolve.tbl_probem (

but the ALTER command is trying to reference a table: tbl_problem

REFERENCES tbl_problem(id) 

Delete l from problem to solve this problem.