[英]Using results from one MySQL query to insert into another query
I am trying to use PHP and MySQL to automatically generate a list like this. 我试图使用PHP和MySQL自动生成这样的列表。
Subject #1 主题#1
Subject #2 主题#2
etc. 等等
Here are the tables: 以下是表格:
eresources eresources
subjects 主题
subjectmap subjectmap
Here is the code that successfully gives me all the subjects in alphabetical order: 以下是按字母顺序成功提供所有主题的代码:
$subjectQuery = "SELECT * FROM subjects WHERE sid != 17 ORDER BY stitle ASC";
$subjectResult = $mysqli->query($subjectQuery);
while ($subjectArray = $subjectResult->fetch_assoc()) {
print "<h5 class='subcategory'>" . $subjectArray['stitle'] . "</h5>";
print "<div class='inner'>
// Need a list of resources that match each subject ID (sid) here!
</div>";
}
Now, here is the code that successfully gives me all the e-resources with a fixed subject ID: 现在,这里的代码成功地为我提供了具有固定主题ID的所有电子资源:
$getERBySubjectQuery = " SELECT erid FROM subjectmap WHERE sid=11 ";
$getERBySubjectResult = $mysqli->query($getERBySubjectQuery);
if($getERBySubjectResult && $getERBySubjectResult->num_rows >= 1){
while($getERBySubjectArray = $getERBySubjectResult->fetch_assoc() ){
$query = " SELECT * FROM eresources WHERE erid = " .$getERBySubjectArray['erid']. " ORDER BY ertitle ASC ";
$result = $mysqli->query($query);
if($result && $result->num_rows >= 1){
while($array = $result->fetch_assoc() ){
print("<a href=\"" . $array['link'] . "\">" . "<h5 class='subcategory'>" . $array['ertitle'] . "<div class='accessnote'>" . $array['access'] . "</div></h5></a>");
}}}}
Naturally, I am not inclined to duplicate the same stanza for each subject ID (sid). 当然,我不倾向于为每个主题ID(sid)复制相同的节。 I want the list of subjects to be generated automatically and the list of resources that have that subject to be generated automatically as well.
我希望自动生成主题列表,并自动生成具有该主题的资源列表。
Basically I need to feed the sid from the first stanza into the second stanza for each subject. 基本上我需要将sid从第一节提供给每个主题的第二节。
You can't do this in MySQL without executing n+1
queries where n
is the number of subjects. 如果不执行
n+1
查询,则不能在MySQL中执行此操作,其中n
是主题数。
You could just use a JOIN
and some clever sorting. 你可以使用
JOIN
和一些聪明的排序。
SELECT
subject.stitle, eresource.etitle
FROM subject
LEFT JOIN subjectmap ON subject.id = subjectmap.sid
LEFT JOIN eresource ON eresource.id = subjectmap.erid
ORDER BY subject.stitle, eresource.etitle
You will get a result like: 您将得到如下结果:
+------------+--------------+
| stitle | etitle |
+------------+--------------+
| Subject #1 | Resource #3 |
| Subject #1 | Resource #5 |
| Subject #1 | Resource #12 |
| Subject #2 | Resource #1 |
| Subject #2 | Resource #4 |
| Subject #2 | Resource #7 |
+------------+--------------+
By using a WHERE clause instead, I think Frits van Campen's query could be more human readable, especially for a beginner : 通过使用WHERE子句,我认为Frits van Campen的查询可能更具人性化,特别是对于初学者:
SELECT subject.stitle, eresource.etitle
FROM subject,subjectmap,eresource
WHERE subject.id = subjectmap.sid
AND eresource.id = subjectmap.erid
ORDER BY subject.stitle, eresource.etitle
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