Retrieve data from multiple tables - php

Question

I have 3 tables, want to write the select result but I don't know how to use 'join' 'inner' 'outer', etc, would be grateful if someone help me.
Tables: manufacturers / products / products_description
$manufacturer_query = "SELECT manufacturers_id from manufacturers WHERE manufacturers_name='" . $m ."'";
$manufacturer = mysql_query($manufacturer_query);
$mresult = mysql_fetch_array($manufacturer);
$products_query = "SELECT p.products_id, pd.products_description FROM products p, products_description pd WHERE p.products_id=pd.products_id AND p.manufacturers_id=" . $mresult['manufacturers_id'];
$products = mysql_query($products_query);
$presult = mysql_fetch_array($products);
$c = 0;
while ($presult){
$c++;
echo $c . ' - ' . $prod['p.products_id'] . ' - '.$prod['pd.products_description'].' - ' . $mresult['manufacturers_id'] . '<br>';
}

Answer 1

For your second query ($products_query), you already have a join.
The comma between the two table names (products and products_description) is a join operator.
This could be rewritten, replacing the comma join operator with the the JOIN keyword, and relocating the join predicate into an ON clause e.g.
SELECT p.products_id
, pd.products_description
FROM products p
JOIN products_description pd
ON pd.products_id=p.products_id
AND p.manufacturers_id = 1
This is an "inner" join in that rows for p.manufacturers_id = 1 will be returned ONLY if (at least one) row exists in the products table that matches that, AND if there is also at least one row in the products_description table that has a value in products_id that matches a row (or rows) returned from the products table.
Adding the keyword INNER before the JOIN keyword does not change the statement, it has no effect.
Given these table contents:
TABLE: products
manufacturers_id products_id
1 222
1 333
1 444
TABLE: products_description
products_id products_description
222 foo
444 fee
444 fi
444 fo
444 fum
That query would return:
p.products_id pd.products_description
222 foo
444 fee
444 fi
444 fo
444 fum
If you add the LEFT keyword before the JOIN keyword, then the query would be an OUTER join, and the query would also return a row like:
p.products_id pd.products_description
333 (NULL)
where a row from the table on the left side of the JOIN has no matching row found in the table on the right side.
If you want the rows returned in a particular sequence, then include an ORDER BY clause at the end of your query, e.g:
ORDER BY p.products_id, pd.product_description
Absent that, MySQL is free to return the rows in an arbitrary order.
The keywords INNER and OUTER are entirely optional. They have no effect on how the statement is processed, and this is why most SQL developers omit these keywords.
A LEFT JOIN is an OUTER join. Rows will be returned from the table on the left even when no matching row is found in the table on the right.
(For a cross join, we do usually include the CROSS keyword, even though it has no effect, just because it serves as documentation that the omission of an ON clause is intentional.)
The call to mysql_fetch_array should be in the loop:
$products = mysql_query($products_query);
$c = 0;
while ($prod = mysql_fetch_array($products) ) {
$c++;
echo $c . ' - ' . $prod['products_id'] . ' - '.$prod['products_description'].' - ' . $mresult['manufacturers_id'] . '<br>';
}
The mysql_ interface is DEPRECATED. New development should use either the mysqli_ or PDO interface.

Answer 2

try this with INNER JOIN
$manufacturer_query = "SELECT m.manufacturers_id , p.products_id, pd.products_description FROM manufacturers m
INNER JOIN products p ON p.manufacturers_id= m.manufacturers_id
INNER JOIN products_description pd ON p.products_id=pd.products_id
WHERE manufacturers_name='" . $m ."'";
$products = mysql_query($manufacturer_query);
$presult = mysql_fetch_array($products);
$c = 0;
while ($presult){
$c++;
echo $c . ' - ' . $prod['p.products_id'] . ' - '.$prod['pd.products_description'].' - ' . $mresult['manufacturers_id'] . '<br>';
}
EDIT
$manufacturer_query = "SELECT m.manufacturers_id mm, p.products_id pp, pd.products_description ppd FROM manufacturers m INNER JOIN
products p ON p.manufacturers_id= m.manufacturers_id INNER JOIN
products_description pd ON p.products_id=pd.products_id WHERE manufacturers_name='" . $m ."'";
$products = mysql_query($manufacturer_query);
$c = 0;
while ($presult = mysql_fetch_array($products)){
$c++;
echo $c . ' - ' . $presult['pp'] . ' - '.$presult['ppd'].' - ' . $presult['mm'] . '<br>';
}