php - 如何统计mysql的行数？

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>";
        }

    ?>

我试图在表中显示特定用户拿走的书籍数量。我使用了 mysqli_num_rows 查询，但它返回 View 中的总行数。我想将每个用户拿走的书籍数量显示为表格数据。请帮忙。

Answer 1

您在 SQL 语句中使用 GROUP BY 进行聚合(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`