Cannot correctly declare variable in procedure loop - mysql

Question

This is driving me bananas. I'm not a mysql guru by any stretch. My goal is to add a large number of columns to a table. I've tried this several ways and the procedure chokes on the DECLARE #FooA NVARCHAR(MAX);. No clue as to why.
I appreciate any pointers...
USE mydatabase;
DELIMITER $$
DROP PROCEDURE IF EXISTS RepeatLoopProc$$
CREATE PROCEDURE RepeatLoopProc()
BEGIN
DECLARE x INT;
DECLARE sn VARCHAR(30);
DECLARE dr VARCHAR(48);
DECLARE #FooA NVARCHAR(MAX);
SET x = 0;
WHILE (x <= 150) DO
SET sn = CONCAT('drivesn_', x);
SET dr = CONCAT('driveinf_', x);
SET x = x + 1;
SET #FooA = 'ALTER TABLE DRIVE_MASTER ADD ' + sn + ' VARCHAR(30), ADD ' + dr + ' VARCHAR(48)';
EXEC sp_executesql #FooA;
END WHILE;
END$$
DELIMITER ;
When I do this I get:
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '#FooA NVARCHAR(MAX);
My forehead is getting flat from slamming it into my desk.
The ultimate goal is adding columns drivesn_0, driveinf_0, drivesn_1, driveinf_1, etc all the way out to drivesn_150 and driveinf_150. Type VARCHAR(30) and VARCHAR(48) for each respectively.

Answer 1

#variables are not DECLAREd and declared variables' identifiers do not start with #.
Also, ALTER statements typically recreate a table behind the scenes (equivalent to something like CREATE TABLE newversion... INSERT INTO newversion SELECT * FROM oldversion ... DROP TABLE oldversion ... RENAME newversion). So you'd be much better off building up a single ALTER statement within the loop, and executing it only once.
Example:
...
SET #FooA = 'ALTER TABLE DRIVE_MASTER';
SET x = 0;
WHILE (x <= 150) DO
SET sn = CONCAT('drivesn_', x);
SET dr = CONCAT('driveinf_', x);
SET #FooA = CONCAT(#FooA
, CASE WHEN x != 0 THEN ', ' ELSE '' END
, 'ADD ', sn, ' VARCHAR(30), ADD ', dr, ' VARCHAR(48)'
);
SET x = x + 1;
END WHILE;
EXEC sp_executesql #FooA;
...
... but what Barmar said in comments is good advice, you should probably just have another table, something like DRIVE_MASTER_DETAILS(x int, sn VARCHAR(30), dr VARCHAR(48))

Answer 2

I already have multiple tables. Basically I am using this to catalog drive serial numbers in hosts. Host can have up to 150 drives. Other tables contain network interface information (macaddrs, etc). All tied together by a common index value. For a system with 150 disk drives I cannot see another way other than 150 columns. Either that or I am missing a fundamental concept.