send records in two separate tables [duplicate]

Solution 1:

Use 2 queries, not one. Of course it must be parameterized queries.

$stmt = $pdo->prepare("insert into comments (user_id,comment) values(?,?)");
$stmt->execute([$user_id,$comment]);

$stmt = $pdo->prepare("insert into comments2 (user_id,comment) values(?,?)");
$stmt->execute([$user_id,$comment]);

is all the code you need.