Question

这是部门表

department_id | department_name
1               computers
2               maths
3               physics
4               mba

这是讲师表

instructor_id | department_id | name
1               1               abc
2               2               manu
3               2               raju
4               3               jaya
5               4               man

从上面的代码中如何显示每个部门的教师总数？

查询是什么？请帮忙。

我是在codeigniter中做的。

Answer 1

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Pack Of Pepper

Answer 2

SELECT COUNT(i.instructor_id) as `instructor_count`, d.department_name
FROM instructor AS i
JOIN department ON d.department_id = i.department_id
GROUP BY i.department_id"

Answer 3

您可以尝试从我的解决方案中进行概念化，看看它是否有帮助，

为避免并发症，您可以直接进行

<?php
//connection
$link = mysqli_connect("localhost","root","","database_name") or die("Couldn't make connection.");

$computer_department_id = //the value
$query = mysqli_query($link, "SELECT  department_id FROM instructure_table WHERE department_id='$computer_department_id')");
$total = mysqli_num_rows($query); 

echo $total; //this one will display the total number of instructors in computer department
?>

或者如果你喜欢

<?php
//connection
$link = mysqli_connect("localhost","root","","database_name") or die("Couldn't make connection.");

$computer_department = //the value
$query = mysqli_query($link, "SELECT  department_id 
FROM instructure_table AS t
WHERE EXISTS (SELECT department_id 
              FROM department_table AS d
              WHERE d.department_id  = t.department_id AND department_id='$computer_department')");
$total = mysqli_num_rows($query); 

echo $total; //this one will display the total number of instructors in computer department
?>

因此，如果您将查询放在部门行

中

department_id | department_name
1               computers        //the query
2               maths            //the query
3               physics          //the query
4               mba              //the query

即使部门的查询位于重复区域，它仍然适用于您。问候

如何显示每个部门的教师总数？ SQL查询

3 个答案: