Question

我尝试了其他几个答案，但我仍然无法理解这一点。也许如果我的具体问题得到解决，我可以理解如何加入三个表格。

我有这些表格：

invoice
id - 

invoiceItem
id - invId - itemId - discode

item
id - name - cid(categoryID) - price - memprice - attendee_price

category
id - catName

我查询发票并获取id，然后运行while循环：获取发票项目列表，按ID列出这些项目的详细信息，按ID获取类别。

这是我正在尝试的查询但挂起了连接和where子句

while ($r = mysql_fetch_assoc($invoice_query){      
//my invoice id is $r['id']

    $iQ = mysql_query("SELECT 
          item.id, item.cid, item.name, item.memprice, item.attendee_price, item.price,
          invoiceItem.discode, 
          categories.id, categories.catName
          FROM invoiceItem 
          INNER JOIN categories ON item.cid=categories.id 
          INNER JOIN item ON ?????? 
          WHERE invoiceItem.id='$r[id]'");
}

Answer 1

INNER JOINS的ON条件通常包含 leftTable.foreignKey = rightTable.primaryKey ...在您的情况下，您需要为发票表添加联接，以便将其主键与invoiceItem表(invoice.id = invoiceItem.invId)中的外键匹配

SELECT 
          item.id, item.cid, item.name, item.memprice, item.attendee_price, item.price,
          invoiceItem.discode, 
          categories.id, categories.catName
          FROM invoiceItem 
          INNER JOIN item ON item.id = invoiceItem.itemId 
          INNER JOIN categories ON item.cid=categories.id 
          INNER JOIN invoice ON invoice.id = invoiceItem.invId
          WHERE invoice.id='$ir[id]'

具有一个已知变量的3个表上的内连接

1 个答案: