使用PHP将SQL Join语句放入HTML表中的单个字段

Question

so i'm creating a schedule system and i'm trying to display the information for the appointment and also, userID's for those who have booked a possition.

I have created a table for Students, Classes and ClassAssosication where the ClassID and UserID are PK And FK from the other tables. I have created a join statement =

SELECT classes.ClassName, students.UserID
    FROM classassociation
    JOIN students
        ON classassociation.UserID = Students.UserID
    JOIN classes
        ON classassociation.ClassID = classes.ClassID
    WHERE classassociation.ClassID = 1;

Where it retrieves the UserID and ClassName for those who have booked a place for Class with the ID = 1 .

I am trying to create a PHP/HTML table where in a field for example, Monday 9AM, i can print out the join statement, for example, Methodology, 1 ,2 (user Id's).

Day     |        9AM       | 10AM
Monday  | Methodology, 1,2 |
Tuesday |                  |

I need this done for multiple classes but trying to attempt one for now. I am unsure of how to do this, so any help will be appreciated. Thank you.

Answer 1

Your query as written will return a row for each ClassName/UserId pair - if there are two people in the methodology class there will be two rows in your query result.

You can choose to combine them in a loop in php, or you can alter your query to group things together. If you think of it as "I want to group all the UserIds for a given classname", it suggest how to use the GROUP BY clause in your SQL:

SELECT classes.ClassName, students.UserID
FROM classassociation
JOIN students
    ON classassociation.UserID = Students.UserID
JOIN classes
    ON classassociation.ClassID = classes.ClassID
WHERE classassociation.ClassID = 1
GROUP BY ClassName;

Now there will be one row for each ClassName, but you still need to tell MYSQL how to handle the multiple UserIds for each row. In your case, you want to have the UserIds joined together in a comma-separated list. Happily, there's a special section in the manual just for the functions you use with GROUP BY . In this case GROUP_CONCAT gives the desired result:

SELECT classes.ClassName, GROUP_CONCAT(students.UserID SEPARATOR ',') AS UersIds
FROM classassociation
JOIN students
    ON classassociation.UserID = Students.UserID
JOIN classes
    ON classassociation.ClassID = classes.ClassID
WHERE classassociation.ClassID = 1
GROUP BY ClassName;

Now you will get a result set with one row for each ClassName , with two columns:

ClassName   | UserIds
---------------------
Methodology | 1,2

Then you can write a simple php loop to take each row in the query and generate a table row in your html.

If you look at the manual for GROUP_CONCAT , you can see that you can also set the order that the userIds are grouped in, which might be useful.

The php loop is pretty simple once you have your query results; you just need to create a table and then add a row for each result:

/*assume your mysql query has returned an array of objects named $result */

// in your html document, create your table with its header
print '<table><thead><tr><th>Class Name</th><th>UserIds</th></tr></thead>';
print '<tbody>';
// now loop through your query results and put stuff into the table
// of course you can monkey around with the table format and what goes in each cell
foreach($result as $row) {
    print '<tr><td>'.$row->ClassName.'</td><td>'.$row->UserIds.'</td></tr>';
}
print '</tbody></table>';

That's a very simple example, but hopefully demystifies the process somewhat.

Your particular case looks like the query is actually to get the contents of one cell in your table; you can either do a much grander query that groups by time and day of week, or you can do little queries and store the results in nested arrays that model how you want your table to look. The html output is structurally the same, but you would have a php loop for each table cell.

To have table with each cell showing the result of a separate query, consider something like the following pseudocode:

$days = array('Monday', 'Tuesday',...'Friday');
$times = array('9', '10'...);

$weekResults = array();
foreach($days as $day) {
    $weekResults[$day] = array();
    foreach($times as $time) {
        $weekResults[$day][$time] = doQuery($day, $time);
    }
}

// now you have nested arrays with a result set for each table cell. 
// Rendering the table, you just use the same loops:

renderTableHeader(); // all the <table><thead> stuff
foreach($weekResults as $day) {
    print '<tr>'
    foreach($day as $time) {
        print '<td>';
        // output the data from your query like above
        // if the formatting is complex, you can even put another table inside the <td>.
        print '</td>';
    }
    print '</tr>';
}
renderTableFooter(); // close tbody and table tags

Hope that helps!