Question

I have two tables in my database.

cat – catid, catname
articles – id, catid, content

so what i want to display is category name (catname) and how many articles are there in that category.

This is my code but it dosent work.

$query = "SELECT cat.cname,  COUNT(articles.cat_id)".
"FROM cat, articles ".
    "GROUP BY cat_id";

$result = mysql_query($query) or die(mysql_error());

while($row = mysql_fetch_array($result)){
    echo $row['cname']. " - ". $row['COUNT(cat_id)'];
    echo "<br />";
}

Any help will be most aprriceated. thanks.

Answer 1

So this is a 1:many relationship. i.e. 1 Category -> Many articles.

The best way to do this is to create a third table, an adjacency list.

Keep your ‘category_id’ and ‘article_id’ unique in tables ‘cat’ and ‘article’.

In your third table you define the 1 : many relationships.

Table 3: cat_articles

adj_id    cat_id    art_id
1         1         1
2         1         2
3         2         3
4         2         4
5         3         5

Now join the tables:

$sql = "SELECT * FROM `cat_articles` adj ".
       "LEFT JOIN (`cat` cat, `articles` art)".
       "ON (cat.cat_id = adj.cat_id AND art.art_id = adj.art_id) ";

This takes the adjacency table, preserves it’s format(due to left join) and appends the tables article and category to it, giving you a categorised table of all your articles. You can now use mysql_fetch_array() to get your results.

Edit: reference first comment, displaying number of rows

You can either, as you have done, use SQL’s function COUNT to return a count of a specific column.

Or, with PHP, run the query, and then use mysql_num_rows($result) to return the number of rows SQL has in its buffer.

Alternatively, retrieve results using mysql_fetch_array($result) and use count to return the number of paired values in the array.