如何在SQL查詢中使用SQL查詢

Question

我有兩個表：

1. 表類別（CAT_ID，類別）
2. 表category_details（CAT_ID，ID，...）

我有SQL代碼像波紋管：

$sql=mysql_query("select * from category"); 
while($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); 

} 

我可以這樣使用嗎？

Answer 1

使用JOIN。

例

SELECT * FROM category LEFT JOIN 
    category_details ON category_details.cat_id = category.cat_id; 

上面的查詢將返回所有的category和相關category detail。

OP評論響應

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); 

完整代碼

<?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表

產品分類表

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'); 

產品表

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); 

上面會輸出

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

您是否希望使用COUNT與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 

這將返回每個類別與其關聯的category_details的計數。使用LEFT JOIN將返回所有類別 - 如果只需要那些具有詳細信息的用戶，則替換爲INNER JOIN。