MySQL的選擇，其中，如果變量設置

Question

我有兩個表：

• 銷售
• sales_sizes

我想通過變量約束sales_sizes做一個查詢$性別，$類別和$品牌。

如果設置了各個變量，如何設置where語句，如果未設置，請不要在查詢中包含它們？

[括號內的僞代碼]

SELECT size, country 
FROM `sales_sizes` WHERE sale_id IN (
    SELECT sale_id 
    FROM `sales` 
    WHERE [gender = $gender if $gender isset] 
    AND [category = $category if $category isset] 
    AND [brand = $brand if $brand isset] 

) 

Answer 1

您可以收集你的變量爲數組，然後處理它是這樣的：

$gender = 'f'; 
$category = null; 
$brand = 'foo'; 

$rgCondition = ['gender'=>$gender, 'category'=>$category, 'brand'=>$brand]; 
$rgCondition = array_filter($rgCondition, function($x) 
{ 
    //strip null-ed values: 
    return isset($x); 
}); 
$rgWhere  = []; 

foreach($rgCondition as $sField=>$mValue) 
{ 
    $rgWhere[] = '`'.$sField.'` = "'.$mValue.'"'; 
} 
$sWhere = count($rgWhere)?' WHERE '.join(' && ', $rgWhere):''; 
//var_dump($sWhere); 

-I've跳過字符串逃跑，但不要忘記它。

Answer 2

使用CASE語句 更新：以前的語法（如由少數人指出）不起作用。您可以按如下方式使用CASE：

SELECT size, country 
FROM `sales_sizes` WHERE sale_id IN (
    SELECT sale_id 
    FROM `sales` 
    WHERE [gender = $gender if $gender isset] 
    AND [category = $category if $category isset] 
    AND [brand = $brand if $brand isset] 

) 

WHERE gender 
    CASE WHEN gender ($gender) = isset THEN 
    $gender 
    ELSE 
    $gender='NULL' 
    END