At PHP script MySQL query is returning NULL column

Question

I have this sql query:

SELECT * 
FROM products p, products_description pd, products_to_categories c left 
     join  products_sex ps on (c.products_id = ps.products_id), 
     categories cc 
WHERE p.products_id = pd.products_id 
      and p.products_id = c.products_id 
      and cc.categories_id = c.categories_id 
      and p.products_status = 1 
      and p.products_price >= 15.8333333333 
      and p.products_price <= 40 
      and p.products_quantity > 0 
      and (ps.products_sex = "U" or ps.products_sex is null) 
      and (c.categories_id = 77 or cc.parent_id = 77) 
ORDER BY products_sort_order, p.products_date_added desc, pd.products_name ASC 
LIMIT 0, 40

If I execute it at MySQL client (command line or Navicat), I get this result:

products_id  |  dodavatelia_id  ...
2153         |  67              ...

But if I get products by PHP script (with mysql_query and mysql_fetch_assoc), I get:

array ( 
    'products_id' => NULL,  
    'dodavatelia_id' => '67', 
    ...
);

Why am I getting the products_id NULL?

koopajah · Accepted Answer · 2013-02-09 10:00:18Z

2

This might be because you are joining multiple tables that contains column with the same name, here products_id so you retrieve the value of the last column with this name that might be NULL.

You should put an alias for the column you want to retrieve :

SELECT p.products_id AS pPropId, p.* FROM products p, ...

Then in your PHP result you can access your column like this:

$result['pPropId']

More info on the SQL Alias functionality here.

EDIT: Why does it work in the command line and not here?

The SQL query works fine and will return each column of name products_id. The issue is that you use mysql_fetch_assoc() that returns an associative array based on your result. And you can't have multiple values for the same key in the array.

So what it might do internally is set $result['products_id'] = p.products_id but then it does the same for the next column with the same name erasing the previous value. You could use mysql_fetch_row() which does not have this issue.

A good practice is to list the columns you really want to retrieve in your SELECT and not just SELECT *. Then it becomes logical that two columns with the same name need different aliases.

edited Feb 9, 2013 at 10:00

answered Feb 9, 2013 at 9:39

koopajah

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2 Comments

yetty Over a year ago

Thank you, this was it. But I don't understand, why it works in mysql command line and in PHP doesn't.

koopajah Over a year ago

@yetty > Because the SQL query works fine. Check my updated answer

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