how to use sql query in sql query - php

Question

I have two tables:
table category(cat_id,category)
table category_details(cat_id,id,...)
I have sql code like bellow:
$sql=mysql_query("select * from category");
while($rows=mysql_fetch_array($sql)){
$id_count=$rows['cat_id'];
$sql1=mysql_query("select * from category_details where cat_id='$id_count'");
$count=mysql_num_rows($sql1);
}
Can I use like this?

Answer 1

Use JOIN.
Example
SELECT * FROM category LEFT JOIN
category_details ON category_details.cat_id = category.cat_id;
above query will return all the category and associated category detail.
OP Comment Response
SELECT c.name,
IFNULL(sub_c.total, 0) num
FROM category c
LEFT JOIN ( SELECT COUNT(*) total, cat_id
FROM category_details
GROUP BY cat_id
) sub_c ON (sub_c.cat_id = c.cat_id);
Complete Code
<?php
$query = "SELECT c.name,
IFNULL(sub_c.total, 0) num
FROM products_category c
LEFT JOIN ( SELECT COUNT(*) total, cat_id
FROM product
GROUP BY cat_id
) sub_c ON (sub_c.cat_id = c.id)";
$result = mysql_query($query)or die(mysql_error());
echo "<table><tr><td>NameCount</td></tr>";
while($row = mysql_fetch_assoc($result))
{
echo "<tr><td>".$row['name']."(".$row['num'].")"."</td></tr>";
}
echo "</table>";
?>
MySQL Table
ProductCategory Table
CREATE TABLE IF NOT EXISTS `products_category` (
`id` int(11) NOT NULL,
`name` varchar(200) COLLATE utf8_unicode_ci NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
--
-- Dumping data for table `products_category`
--
INSERT INTO `products_category` (`id`, `name`) VALUES
(1, 'Erasmus'),
(2, 'Preston'),
(3, 'Ulric'),
(4, 'Gray'),
(5, 'Joseph'),
(6, 'Merrill'),
(7, 'Alan'),
(8, 'Jeremy'),
(9, 'Solomon'),
(10, 'Andrew'),
(11, 'Galvin'),
(12, 'Craig'),
(13, 'Cameron'),
(14, 'Omar'),
(15, 'Addison');
Product Table
CREATE TABLE IF NOT EXISTS `product` (
`id` int(11) NOT NULL,
`name` varchar(200) COLLATE utf8_unicode_ci NOT NULL,
`cat_id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
--
-- Dumping data for table `product`
--
INSERT INTO `product` (`id`, `name`, `cat_id`) VALUES
(1, 'Wesley', 1),
(2, 'Graiden', 2),
(3, 'Cruz', 5),
(4, 'Hayden', 5),
(5, 'Kennedy', 6),
(6, 'Uriah', 8),
(7, 'Alan', 8),
(8, 'Cade', 1),
(9, 'Ryan', 5),
(10, 'Brody', 7);
Above will output
Erasmus(2)
Preston(1)
Ulric(0)
Gray(0)
Joseph(3)
Merrill(1)
Alan(1)
Jeremy(2)
Solomon(0)
Andrew(0)
Galvin(0)
Craig(0)
Cameron(0)
Omar(0)
Addison(0)

Answer 2

Are you looking to use COUNT with GROUP BY:
select c.cat_id, c.cat_name, count(cd.*)
from category c
left join category_details cd
on c.cat_id = cd.cat_id
group by c.cat_id, c.cat_name
This will return each category with the count of category_details associated with it. Using LEFT JOIN will return all categories -- replace with an INNER JOIN if you want only those with details.