What potential issues can arise when migrating from MySQL 4.0 to MySQL 5 in PHP applications?

One potential issue when migrating from MySQL 4.0 to MySQL 5 in PHP applications is the deprecated use of the "TYPE" keyword in table creation queries. This keyword has been replaced by "ENGINE" in MySQL 5. To solve this issue, simply update your table creation queries to use the "ENGINE" keyword instead of "TYPE".

// Before migration
$query = "CREATE TABLE users (id INT NOT NULL AUTO_INCREMENT, name VARCHAR(50), PRIMARY KEY (id)) TYPE=InnoDB";

// After migration
$query = "CREATE TABLE users (id INT NOT NULL AUTO_INCREMENT, name VARCHAR(50), PRIMARY KEY (id)) ENGINE=InnoDB";