The number of rows in table1 records can be obtained, but the number of fields in table1 cannot be obtained. Why?

Question

$p1 = new DB();
$p2 = $p1->runSQT("select * from `table1`");
         
$h1 = $p2->num_rows; //The number of record rows in the table
$z1 = $p2->num_fields; //The number of fields in the table

Answer 1

What are you asking about, which course it is in, can you give the complete code? It is a fragment, difficult to analyze