Php 使用PDO获取一个MySQL数据库列中有多少个项目实例的列表

我已经在许多论坛和问题上滔滔不绝，这些问题与我试图实现的目标类似（但不尽相同）。我正在将旧的mysql查询更新为PDO。我看到很多人在PDO中使用COUNT（*）时遇到问题，还有一些帖子解释了如何使用query（）而不是fetch（），或者使用rowCount（）有时使用fetchColumn（）

但是，它们似乎用于检查查询是否返回查询中的任何行或零行。可以测试一个查询是否有效，或者返回一行，列出单个查询返回的行数？这不是我想要做的（或者我看错了）

我想要完成的是获得一个列表，其中列出了给定列中每个唯一项出现的次数。我有一个彩弹网站，我想列出多少项目，我为每个类别。旧的mysql代码（为了简洁起见被剪掉）是这样的：

    $query = "SELECT Category, COUNT(*) FROM table WHERE Notes NOT LIKE 'Discontinued' GROUP BY Category";
    $result = mysql_query($query);
    $num_results = $result->num_rows;

    while($row=mysql_fetch_array($result, MYSQL_NUM)) {
    echo "$row[0]: $row[1]<br />";
    }

$query=“从表中选择类别，计数（*），其中注释不类似于“已终止”类别分组”；
$result=mysql\u query（$query）；
$num\u results=$result->num\u行；
而（$row=mysql\u fetch\u数组（$result，mysql\u NUM））{
回显“$row[0]：$row[1]
”；
}

我的结果是：

空气：312
标记：627
口罩：124
油漆：97
等等等等

因此，现在我正试图用PDO获得同样的结果，并尝试了从其他人提出的问题中得出的十几条不同的建议。我通常喜欢自己解决这些问题，这是我第一次不得不认输并在PHP论坛上发布我自己的问题。我把自己弄糊涂了，不知道该往哪条路走了

---

如果您能从全新的角度提供指导，我们将不胜感激。一定有一种我看不见或误解的方式。提前谢谢

对于任何可能正在为这个概念而挣扎的人，这里是我到目前为止想到的。我相信有更干净的方法可以做到这一点，但目前看来效果不错。由于我还试图将更多面向对象的编码融入到我的技巧包中，因此我最终将解决方案的业务端放入了一个函数中。如果我在重建我的站点时积累了更多，我可能最终会将它们组合到一个PDO包装类中，或者类似的性质

以下是我的功能：

function fieldCount($field,$condition,$table)
{
//This is just a file that holds the database info and can be whatever name you want
require('database.ini');
try{
    $dbh = new PDO("mysql:host=$db_hostname;dbname=$db_database", $db_username, $db_password);

    //This turns on the error mode so you get warnings returned, if any
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $stmt = $dbh->prepare("SELECT $field, COUNT(*) AS count FROM $table $condition GROUP BY $field");

// I tried to bind my $field variable but for some reason it didn't work so I
// commented it out below until I can look deeper into it. If anyone sees any
// glaring errors, please point them out. It looks right to me, but as I said,
// it's not working.

//  $stmt = $dbh->prepare("SELECT :field, COUNT(*) AS count FROM $table $condition GROUP BY :field");
//  $stmt->bindParam(':field', $field);

    $stmt->execute();

    $results=$stmt->fetchAll(PDO::FETCH_ASSOC);
    // Creates an array similar as the following:
    // $results[0][$field] $results[0]['count']
    // $results[1][$field] $results[1]['count']
    // $results[2][$field] $results[2]['count']
    // with each row as an array of values within a numeric array of all rows

    $dbh = null;
}
catch(PDOException $e)
{
echo $e->getMessage();
}

return $results;
}

<?php
// First you have to "require" your file where the function is located,
// whatever you name it.
require('FieldCountFunction.php');

// Determine what column in your database you want to get a count of.
// In my case I want to count how many items there are in each individual
// category, so the $field is Category here.
$field = 'Category';

// If there is a condition to your query, you would state it here.
// In my case I wanted to exclude any items in my Inventory table that
// are marked "Discontinued" in the Notes column of my database.
$condition = "WHERE Notes NOT LIKE 'Discontinued'";

$DB_Table = 'Inventory';

// Now you call the function and enter the $field you want to get a count of,
// any conditions to the query, and the database table name you are querying.
// The results you collected in the function (it was called $results above),
// will be dumped into a new array now called "$fieldArray" below.
$fieldArray = fieldCount($field, $condition, $DB_Table);

// To get the data out again you can do the following to cycle through the
// numeric array of rows (that's what the "$i" is for) and from each numbered
// row you can retrieve the "$field" and "count" that you need. Then display
// them however you want. I'll just echo them out here.
$i=0;
while($i<count($fieldArray))
{
    echo $fieldArray[$i]["$field"].' : '.$fieldArray[$i]['count'].'<br />';
    $totalCount = $totalCount + $fieldArray[$i]['count'];
    $i++;
}
echo $totalCount.' items total';
?>

database.ini文件可能看起来很简单，如下所示：

<?php
    //database.ini

    $db_hostname = 'myHostname';
    $db_database = 'databaseNameHere';
    $db_username = 'YourUserNameHere';
    $db_password = 'YourPasswordHere';
?>

以下是调用函数的方式：

function fieldCount($field,$condition,$table)
{
//This is just a file that holds the database info and can be whatever name you want
require('database.ini');
try{
    $dbh = new PDO("mysql:host=$db_hostname;dbname=$db_database", $db_username, $db_password);

    //This turns on the error mode so you get warnings returned, if any
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $stmt = $dbh->prepare("SELECT $field, COUNT(*) AS count FROM $table $condition GROUP BY $field");

// I tried to bind my $field variable but for some reason it didn't work so I
// commented it out below until I can look deeper into it. If anyone sees any
// glaring errors, please point them out. It looks right to me, but as I said,
// it's not working.

//  $stmt = $dbh->prepare("SELECT :field, COUNT(*) AS count FROM $table $condition GROUP BY :field");
//  $stmt->bindParam(':field', $field);

    $stmt->execute();

    $results=$stmt->fetchAll(PDO::FETCH_ASSOC);
    // Creates an array similar as the following:
    // $results[0][$field] $results[0]['count']
    // $results[1][$field] $results[1]['count']
    // $results[2][$field] $results[2]['count']
    // with each row as an array of values within a numeric array of all rows

    $dbh = null;
}
catch(PDOException $e)
{
echo $e->getMessage();
}

return $results;
}

<?php
// First you have to "require" your file where the function is located,
// whatever you name it.
require('FieldCountFunction.php');

// Determine what column in your database you want to get a count of.
// In my case I want to count how many items there are in each individual
// category, so the $field is Category here.
$field = 'Category';

// If there is a condition to your query, you would state it here.
// In my case I wanted to exclude any items in my Inventory table that
// are marked "Discontinued" in the Notes column of my database.
$condition = "WHERE Notes NOT LIKE 'Discontinued'";

$DB_Table = 'Inventory';

// Now you call the function and enter the $field you want to get a count of,
// any conditions to the query, and the database table name you are querying.
// The results you collected in the function (it was called $results above),
// will be dumped into a new array now called "$fieldArray" below.
$fieldArray = fieldCount($field, $condition, $DB_Table);

// To get the data out again you can do the following to cycle through the
// numeric array of rows (that's what the "$i" is for) and from each numbered
// row you can retrieve the "$field" and "count" that you need. Then display
// them however you want. I'll just echo them out here.
$i=0;
while($i<count($fieldArray))
{
    echo $fieldArray[$i]["$field"].' : '.$fieldArray[$i]['count'].'<br />';
    $totalCount = $totalCount + $fieldArray[$i]['count'];
    $i++;
}
echo $totalCount.' items total';
?>

这将产生与以下类似的结果：

附件：638
标记：432
口罩：146
包装：93件
油漆：47
共1356项

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我希望这能帮助其他人。如果有人能解释一下为什么我的装订不起作用，我将不胜感激。如果没有，我相信我最终会找到答案。

您将在PDO中使用相同的查询，并像任何其他查询一样获取结果。。获取“一个项目有多少个实例”没有什么特别的。。这些都是mysql和PDO的结果<代码>$pdo->query（'SELECT COUNT（）作为myTable中的COUNT'）->execute（）->fetch（pdo:：fetch_OBJ）->COUNTSELECT category，count（*）as count…）将为每个唯一的类别返回两个字段和一行。您应该尝试了解

fetch（）

、

fetchAll（）

、

query（）

等之间的区别，并自行决定如何最好地使用它们。盲目地偏离随机博客的建议，而不理解其背后的原因，将不会教会你任何东西。