在 PDO 中动态 WHERE 子句查询后计算特定行数

Question

我正在关注this tutorial，在 PDO 中进行动态 WHERE 子句查询。

假设我有一个简短的教程代码，就像这样：

// always initialize a variable before use!
$conditions = [];
$parameters = [];

// conditional statements
if (!empty($_GET['name']))
{
   // here we are using LIKE with wildcard search
   // use it ONLY if really need it
   $conditions[] = 'name LIKE ?';
   $parameters[] = '%'.$_GET['name']."%";
}

if (!empty($_GET['sex']))
{
   // here we are using equality
   $conditions[] = 'sex = ?';
   $parameters[] = $_GET['sex'];
}


// the main query
$sql = "SELECT * FROM users";

// a smart code to add all conditions, if any
if ($conditions)
{
   $sql .= " WHERE ".implode(" AND ", $conditions);
}

// the usual prepare/execute/fetch routine
$stmt = $pdo->prepare($sql);
$stmt->execute($parameters);
$data = $stmt->fetchAll();

通过添加行$count = $stmt->rowCount();，我可以计算行数。

现在假设我有这样的数据：

| ID | User name    | sex     |
| -- | ------------ | --------|
| 1  | Sandra Smith | female  | 
| 2  | Ben Smith    | male    | 
| 3  | John Lee     | male    | 
| 4  | John Smith   | male    | 

如果我现在搜索“Smith”，我会得到 3 个结果，当我回显 $count 时，会显示数字 3。

问题： 我还想回应我通过完全相同的查询获得了多少女性和男性用户。 我在互联网上进行了很多搜索，但找不到使用 PDO 解决此问题的案例。另外，我不确定是否需要另一个额外的查询来获取女性和男性用户的数量。

Answer 1

在查询中使用 CASE 语句根据条件获取行数：

<?php
// always initialize a variable before use!
$conditions = [];
$parameters = [];

// conditional statements
if (!empty($_GET['name']))
{
   // here we are using LIKE with wildcard search
   // use it ONLY if really need it
   $conditions[] = 'name LIKE ?';
   $parameters[] = '%'.$_GET['name']."%";
}

if (!empty($_GET['sex']))
{
   // here we are using equality
   $conditions[] = 'sex = ?';
   $parameters[] = $_GET['sex'];
}


// the main query
$sql = "SELECT count(*) as count_all,
sum(case when sex  = 'female ' then 1 else 0 end) AS count_female,
sum(case when sex  = 'male ' then 1 else 0 end) AS count_male
FROM users";

// a smart code to add all conditions, if any
if ($conditions)
{
   $sql .= " WHERE ".implode(" AND ", $conditions);
}

// the usual prepare/execute/fetch routine
$stmt = $pdo->prepare($sql);
$stmt->execute($parameters);
$row = $stmt->fetch();

// count all users
$count_all = $row['count_all'];

// count female users
$count_all = $row['count_female'];

// count male users
$count_all = $row['count_male'];

?>

检查：How to get multiple counts with one SQL query?