Databases
StackOverflow2013
Postsdbo
POUsing a join with three tables when a field might be null
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POUsing a join with three tables when a field might be null
    primarykey
    data
    text
    <p>The code below works great. It combines data from two MySQL tables. I would like to modify it by pulling in some data from a third MySQL table called <code>comment</code>. </p> <p>In the HTML table below, <code>title</code> is a field in the MySQL table <code>submission</code>. Every <code>title</code> has a corresponding <code>submissionid</code> field. The field <code>submissionid</code> is also found in the <code>comment</code> MySQL table. </p> <p>In the HTML table below, I would like <code>countComments</code> to equal the number of times a field called <code>commentid</code> appears in the MySQL table <code>comment</code> for any given <code>submissionid</code>,where the <code>submissionid</code> is the same in both the <code>submission</code> and <code>comment</code> tables, and where the <code>submissionid</code> corresponds to the <code>title</code> being used.</p> <p>Here's the catch: if there is no row in the MySQL table <code>comment</code> that corresponds with the <code>submissionid</code> being used for <code>table</code>, I would like <code>countComments</code> to equal to zero.</p> <p>How can I do this?</p> <pre><code>$sqlStr = "SELECT s.loginid, s.title, s.url, s.displayurl, l.username FROM submission AS s, login AS l WHERE s.loginid = l.loginid ORDER BY s.datesubmitted DESC LIMIT 10"; $result = mysql_query($sqlStr); $arr = array(); echo "&lt;table class=\"samplesrec\"&gt;"; while ($row = mysql_fetch_array($result)) { echo '&lt;tr&gt;'; echo '&lt;td class="sitename1"&gt;&lt;a href="http://www.'.$row["url"].'"&gt;'.$row["title"].'&lt;/a&gt;&lt;/td&gt;'; echo '&lt;/tr&gt;'; echo '&lt;tr&gt;'; echo '&lt;td class="sitename2"&gt;&lt;a href="http://www...com/sandbox/members/index.php?profile='.$row["username"].'"&gt;'.$row["username"].'&lt;/a&gt;&lt;a href="http://www...com/sandbox/comments/index.php?submission='.$row["title"].'"&gt;'.$row["countComments"].'&lt;/a&gt;&lt;/td&gt;'; echo '&lt;/tr&gt;'; } echo "&lt;/table&gt;"; </code></pre>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USanalyticalpicasso
    1. USJohn
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POUsing a join with three tables when a field might be null
      1. This table or related slice is empty.
      1. VTUpMod
    1. COwhat is the exact name of the submissionid field in submission and comment tables?
      singulars
      1. POUsing a join with three tables when a field might be null
      1. USUnreason
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload