不知道如何在 PHP 中限制内部 SQL 查询

Question

到目前为止，

大量 S/O 搜索非常有帮助......下面的 almost 有效。我的问题是第二个 SQL 查询 returns ALL the 'ingredients' for EACH 'recipe' -- 而食谱 #1 有成分 A、C、F，而食谱 #2 有成分 A、G、H。如何将第二个查询限制为 return 仅当前循环中配方的成分？如果有 PHP/SQL 向导的帮助，我将不胜感激。

具有多对多关系的数据库结构：

RECIPE (recid, title) 
REC_ING (recid, ingid) 
INGREDIENT (ingid, ingredient)

这是我的 PHP 代码：

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "recipe";
try {
  $db = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
}
catch(PDOException $e) {
   echo "Error: " . $e->getMessage();
}
$xml = new XMLWriter();
$xml->openURI('stackexch.xml');
$xml->setIndent(2);
$xml->startDocument('1.0', 'UTF-8');
$xml->startElement('recipes');
$recipe = $db->query("SELECT * FROM recipe");
foreach ($recipe as $row) {
  $xml->startElement('recipe');
  $xml->startElement('title');
  $xml->writeRaw($row['title']);
  $xml->endElement();
  $ingredient = $db->query("SELECT ingredient FROM recipe, rec_ing, ingredient WHERE recipe.recid=rec_ing.recid AND ingredient.ingid=rec_ing.ingid");
  foreach ($ingredient as $subrow) {
    $xml->startElement('ingredient');
    $xml->writeRaw($subrow['ingredient']);
    $xml->endElement();
    }
  $xml->endElement();
}
$xml->endElement();
$xml->endDocument();
$xml->flush();
?>

下面是 returned:

<?xml version="1.0" encoding="UTF-8"?>
<recipes>
  <recipe>
    <title>Recipe #1</title>
    <ingredient>ingredient A</ingredient>
    <ingredient>ingredient C</ingredient>
    <ingredient>ingredient F</ingredient>
    <ingredient>ingredient G</ingredient>
    <ingredient>ingredient H</ingredient>
  </recipe>
  <recipe>
    <title>Recipe #2</title>
    <ingredient>ingredient A</ingredient>
    <ingredient>ingredient C</ingredient>
    <ingredient>ingredient F</ingredient>
    <ingredient>ingredient G</ingredient>
    <ingredient>ingredient H</ingredient>
  </recipe>
</recipes>

Answer 1

假设recid是菜谱的id。试试这个：

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "recipe";
try {
  $db = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
}
catch(PDOException $e) {
   echo "Error: " . $e->getMessage();
}
$xml = new XMLWriter();
$xml->openURI('stackexch.xml');
$xml->setIndent(2);
$xml->startDocument('1.0', 'UTF-8');
$xml->startElement('recipes');
$recipe = $db->query("SELECT * FROM recipe");
foreach ($recipe as $row) {
  $xml->startElement('recipe');
  $xml->startElement('title');
  $xml->writeRaw($row['title']);
  $xml->endElement();
  $ingredient = $db->query("SELECT ingredient FROM recipe, rec_ing, ingredient WHERE recipe.recid=rec_ing.recid AND ingredient.ingid=rec_ing.ingid AND recipe.recid = " . $row['recid']);
  foreach ($ingredient as $subrow) {
    $xml->startElement('ingredient');
    $xml->writeRaw($subrow['ingredient']);
    $xml->endElement();
    }
  $xml->endElement();
}
$xml->endElement();
$xml->endDocument();
$xml->flush();
?>

由于您已经select从菜谱table中获取，因此您不需要再次select。您可以像这样简化代码：

<?php
    $servername = "localhost";
    $username = "root";
    $password = "";
    $dbname = "recipe";
    try {
      $db = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    }
    catch(PDOException $e) {
       echo "Error: " . $e->getMessage();
    }
    $xml = new XMLWriter();
    $xml->openURI('stackexch.xml');
    $xml->setIndent(2);
    $xml->startDocument('1.0', 'UTF-8');
    $xml->startElement('recipes');
    $recipe = $db->query("SELECT * FROM recipe");
    foreach ($recipe as $row) {
      $xml->startElement('recipe');
      $xml->startElement('title');
      $xml->writeRaw($row['title']);
      $xml->endElement();
      $ingredient = $db->query("SELECT ingredient FROM rec_ing, ingredient WHERE ingredient.ingid=rec_ing.ingid AND rec_ing.recid = " . $row['recid']);
      foreach ($ingredient as $subrow) {
        $xml->startElement('ingredient');
        $xml->writeRaw($subrow['ingredient']);
        $xml->endElement();
        }
      $xml->endElement();
    }
    $xml->endElement();
    $xml->endDocument();
    $xml->flush();
    ?>

通常，我不建议将变量连接到查询中，但在这种情况下它是安全的，因为您已经select从数据库中获取 ID。

Answer 2

这正在消耗资源：

SELECT * FROM recipe

然而你只使用了 [title]，为什么拉所有列？

正在为从上面返回的每一行执行此操作：

SELECT ingredient 
FROM recipe, rec_ing, ingredient 
WHERE recipe.recid=rec_ing.recid AND ingredient.ingid=rec_ing.ingid

但是您可以在一个查询中完成上述两项操作，因此消耗的资源更少：

SELECT r.title, i.ingredient 
FROM recipe r
INNER JOIN rec_ing ON r.recid=rec_ing.recid 
INNER JOIN ingredient i ON i.ingid=rec_ing.ingid

另请注意，25 多年前，ANSI 正式制定了一组您应该尝试采用的联接。 2 个提示：

拒绝自己在 from 子句中 table 的名字和
如果条件有两个 table 引用，则此条件属于 JOIN，例如 recipe.recid=rec_ing.recid（看到了吗？在等号的每一边都有一个 table 引用，这是一个连接条件）

最后一个建议：SQL 查询不必是 PHP 代码中的单行。

Answer 3

欢迎使用 Whosebug。您需要添加 RECIPE.recid='.$row['recid'] 在 where 子句中。

但是在我看来，您可以仅使用一个查询来简化逻辑。我建议使用内部联接来包含来自多个表的信息。

SELECT *
FROM recipe AS r
INNER JOIN rec_ing AS ri ON ri.recid=r.recid
INNER JOIN INGREDIENT AS i ON i.ingid=ri.ingid;

不知道如何在 PHP 中限制内部 SQL 查询

Don't know how to restrict inner SQL query in PHP

php

xml

mysql

xmlwriter