How to count number of rows in mysql?

Question

<?php
        $query="select usertable.id, name, username, dateofbirth, user_id from usertable INNER JOIN passbook on passbook.user_id=usertable.id ";
        $result= mysqli_query($sql, $query);
        $rowcount=mysqli_num_rows($result);
        printf("Result set has %d rows.\n",$rowcount);
        while($row=mysqli_fetch_array($result))
        {
            echo "<tr>";
            echo "<td>";
            echo $row["id"];
            echo "</td>";
            echo "<td>";
            echo $row["name"];
            echo "</td>";
            echo "<td>";
            echo $row["dateofbirth"];
            echo "</td>";               
            echo "<td>";
            echo $row["user_id"];
            echo "</td>";

            echo "</tr>";
        }

    ?>

I am trying to display the number of books taken by a particualar user in the table. I have used the mysqli_num_rows query but it returns the total number of rows in the view. I want to display the number of books taken by each user as a table data. Please help.

Answer 1

您在SQL语句中使用GROUP BY进行了聚合（这不是要解决的PHP问题，而是数据库解决方案）：

select count(*) as bookstaken, usertable.id, name, username, dateofbirth, user_id from usertable INNER JOIN passbook on passbook.user_id=usertable.id GROUP BY usertable.id, name, username, dateofbirth, user_id`

Answer 2

从passbook.user_id = usertable.id上的usertable INNER JOIN存折中选择count（*）作为count，usertable.id，名称，用户名，生日，user_id