Boolean variable always assuming 1 in select...into - MySQL - mysql

Question

I'm doing a stored procedure to update a table and that table has a boolean named: "Finished", as a field. This field informs us if a game is finished. In my problem it makes sense to be able to set something as finished before the expiration date so, because of that, I'm checking if the row to update has the "Finished" field as true or if the expiration date has passed.
SET #isFinished=0;
SELECT Finished INTO #isFinished FROM game WHERE ID = gameID;
-- gameID comes as a parameter
-- date comes as a parameter as well
IF DATEDIFF(STR_TO_DATE(date, "%Y-%m-%d") , CURDATE()) < 0 OR #isFinished<>0 THEN
select CONCAT("Game can't be updated because it's already finished. Days missing:",DATEDIFF( STR_TO_DATE(date, "%Y-%m-%d"), CURDATE() )," and #finished=", #isFinished, ", game=",gameID)
into #msg;
SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = #msg;
END IF;
The problem is that when I try to update an unfinished game it is getting into the if and throwing the error message:
"sqlMessage: 'Game can\'t be updated because it\'s already finished. Days missing:337 and #finished=1, game=2'".
quick note: The variable #isFinished is never used but in this block of code.
I've always assured that the value of "Finished" was 0 before I tested it and yet it keeps selecting it as 1 and, because of that, getting into the if.
I thought it could be from the select...into so I tried it out of the stored procedure (literally copy paste, just changed the "gameID" to the actual ID that I'm using) and it worked perfectly.
SELECT Finished INTO #isFinished FROM game WHERE ID = 2;
SELECT #isFinished
After this, I don't know what more can I check. If anyone could help I'd be thankful.
Isolated test:
create database test;
use test;
create table Tournament(
ID int(10) not null unique auto_increment,
Name varchar(250) not null,
Start_Date date not null,
End_Date date not null,
Primary key(ID)
);
create table Game(
ID int(10) not null unique auto_increment,
Tournament_ID int(10),
Date date,
Finished boolean,
Foreign Key(Tournament_ID) references Tournament(ID) ON DELETE CASCADE,
Primary Key(ID)
);
INSERT INTO Tournament VALUES(NULL, "tournament1", str_to_date("2020-06-01","%Y-%m-%d"), str_to_date("2020-07-01","%Y-%m-%d"));
INSERT INTO Game VALUES(NULL, 1, str_to_date("2020-06-02","%Y-%m-%d"), 0);
DELIMITER $$
DROP PROCEDURE IF EXISTS `UpdateGame`$$
CREATE PROCEDURE `UpdateGame`(IN gameID int, date varchar(10), finished boolean)
BEGIN
SET #isFinished=0;
SELECT Finished INTO #isFinished FROM game WHERE ID = gameID;
IF DATEDIFF(STR_TO_DATE(date, "%Y-%m-%d") , CURDATE()) < 0 OR #isFinished<>0 THEN
select CONCAT("Game can't be updated because it's already finished. Days missing:",DATEDIFF( STR_TO_DATE(date, "%Y-%m-%d"), CURDATE() )," and #finished=", #isFinished, ", game=",gameID)
into #msg;
SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = #msg;
END IF;
UPDATE game SET Date=STR_TO_DATE(date, "%Y-%m-%d"), Finished=finished WHERE ID=gameID;
END$$
call UpdateGame(1,"2020-06-03",1);
SELECT * FROM game;
SELECT Finished INTO #isFinished FROM game WHERE ID = 1;
SELECT #isFinished;

Answer 1

You have IN param Finished so inside your stored procedure, when querying the table, in fact you querying the IN param.
So you need to delete/rename the Finished IN param or write your internal select query as:
SELECT `game`.`Finished`
INTO #isFinished
FROM game
WHERE ID = gameID;
P.S. People usually have some kind of prefixes on input params to distinguish them visually inside the stored procedure from tables, columns of local variables.