Why error occurs when I send multiple queries into mysqli_query?

Question

The same request in the Adminer has no errors, but in php is

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB

Answer 1

You are supposed to run your queries with separate API calls.

$DB->query("INSERT INTO ...");
$DB->query("SET @lastID = LAST_INSERT_ID()");
$DB->query("INSERT INTO ...");

note that you don't actually need the second query here as LAST_INSERT_ID() can be used directly.

Besides, you should never use a function named "HTML speacial chars" for any database interaction. You have to use prepared statements instead.

Note that a suggestion to use multi_query is unjustified and misleading, causing a lot of problems.