MySQL Procedure variable receiving null on count(*) - mysql

Question

Why when I do Select count(*) From table1 I receive 300 but if I do SELECT end = COUNT(*) FROM table1; returns null
Here is the fiddle example https://dbfiddle.uk/ZHzoaztV
code snippet:
CREATE TABLE table1(
start int NOT NULL,
id int PRIMARY KEY AUTO_INCREMENT,
counter int NOT NULL,
difference int NOT NULL,
end int NOT NULL
);
CREATE PROCEDURE doWhile()
BEGIN
DECLARE i INT DEFAULT 1;
DECLARE start INT DEFAULT 120;
DECLARE counter INT DEFAULT 1;
DECLARE end INT DEFAULT 300;
WHILE (i <= end) DO
INSERT INTO table1 VALUES (start,null,counter,start+counter,end);
SET i = i+1;
SET counter = counter+1;
END WHILE;
END;
CALL doWhile();
SELECT * FROM table1;
CREATE PROCEDURE insertMore()
BEGIN
DECLARE start INT;
DECLARE counter INT DEFAULT 1;
DECLARE end INT;
SELECT end = COUNT(*) FROM table1;
SELECT start = MAX(id)+1 FROM table1;
-- SELECT COUNT(*) FROM table1;
WHILE (counter <= end) DO
INSERT INTO table1 VALUES (start,null,counter,start+counter,end);
SET counter = counter+1;
END WHILE;
END;
CALL insertMore();
SELECT * FROM table1;
I expected to return 300, so hopefully my function should do it right

Answer 1

You have a problem with start and end Variable
Can you try this :
CREATE PROCEDURE insertMore()
BEGIN
DECLARE start INT;
DECLARE counter INT DEFAULT 1;
DECLARE end INT;
SELECT COUNT(*) into end FROM table1;
SELECT max(id)+1 into start FROM table1;
-- SELECT COUNT(*) FROM table1;
WHILE (counter <= end) DO
INSERT INTO table1 VALUES (start,null,counter,start+counter,end);
SET counter = counter+1;
END WHILE;
END;
Try it here : https://dbfiddle.uk/X6vP3wKW