How to fix ERROR 1100: Table was not locked with LOCK TABLES in MySQL

-- For example, this query accesses users AND orders tables:
SELECT * FROM users u JOIN orders o ON u.id = o.user_id;

-- Lock all tables before querying them:
LOCK TABLES users WRITE, orders READ;
SELECT * FROM users u JOIN orders o ON u.id = o.user_id;
UNLOCK TABLES;

-- Lock the original table AND each alias:
LOCK TABLES products WRITE, products AS p1 READ;
INSERT INTO products SELECT * FROM products AS p1 WHERE id > 100;
UNLOCK TABLES;

# Create dump without locks (if all tables are InnoDB):
mysqldump --single-transaction --quick my_database > backup.sql

# Or skip locks entirely:
mysqldump --skip-lock-tables my_database > backup.sql

# Restore the dump:
mysql my_database < backup.sql

-- Instead of LOCK TABLES, use transactions:
START TRANSACTION;
UPDATE users SET status = "active" WHERE id = 1;
UPDATE accounts SET balance = balance - 50 WHERE user_id = 1;
COMMIT;

LOCK TABLES my_table WRITE;
ALTER TABLE my_table ADD COLUMN new_col INT;
UNLOCK TABLES;

-- Re-lock before the next ALTER:
LOCK TABLES my_table WRITE;
ALTER TABLE my_table ADD INDEX idx_new_col (new_col);
UNLOCK TABLES;