Question

这是一个解释我需要的例子：

我有3张桌子：

 contact: { id, invoices, name } // a contact can have several invoices
 invoice: { id, contact, lines, comment } // an invoice can have several lines but only one contact
 line: { id, invoice, designation } // a line can have only one invoice

如果用户搜索发票，则想要查询评论，指定和名称字段，并仅获取匹配的发票。

所以我做到了这一点：

SELECT 
  invoice.id AS id, 
  invoice.contact AS contact, 
  invoice.comment AS comment, 
FROM invoice 
  LEFT JOIN contact ON invoice.contact = contact.id 
  LEFT JOIN line ON line.invoice = invoice.id
WHERE (
  contact.name LIKE '%SEARCH_TERM%' OR 
  invoice.comment LIKE '%SEARCH_TERM%' OR 
  line.designation LIKE '%SEARCH_TERM%'
)

这项工作除了如果发票有几行与搜索字词匹配，我会得到相同发票的几倍。

所以我的问题是：即使在几个相关记录中找到搜索词，是否有办法只获得一次发票？

另外，有没有办法只使用发票的字段而不使用ALIAS（除了搜索，我不关心表格的联系和行）？

如果你知道更好的方法，我很乐意听到它。

Answer 1

SELECT 
  DISTINCT invoice.*
FROM invoice 
  LEFT JOIN contact ON invoice.contact = contact.id 
  LEFT JOIN line ON line.invoice = invoice.id
WHERE (
  contact.name LIKE '%SEARCH_TERM%' OR 
  invoice.comment LIKE '%SEARCH_TERM%' OR 
  line.designation LIKE '%SEARCH_TERM%'
)

Answer 2

是。您可以通过向WHERE子句添加子查询来执行此操作：

SELECT invoice.id AS id, invoice.contact AS contact, invoice.comment AS comment, 
FROM invoice LEFT JOIN
     contact
     ON invoice.contact = contact.id 
WHERE contact.name LIKE '%SEARCH_TERM%' OR 
      invoice.comment LIKE '%SEARCH_TERM%' OR
      invoice.id in (select line.invoice
                     from line
                     where line.designation LIKE '%SEARCH_TERM%')

您还可以使用子查询在FROM子句中构造它：

SELECT invoice.id AS id, invoice.contact AS contact, invoice.comment AS comment, 
FROM invoice LEFT JOIN
     contact
     ON invoice.contact = contact.id left join
     (select distinct line.invoice
      from line
      where line.designation LIKE '%SEARCH_TERM%'
     ) line
     on line.invoice = invoice.id
WHERE contact.name LIKE '%SEARCH_TERM%' OR 
      invoice.comment LIKE '%SEARCH_TERM%' OR
      line.invoice is not null

在此构造中，如果多行包含搜索词，则需要distinct关键字以防止重复行。

Answer 3

DISTINCT会起作用吗？

SELECT DISTINCT
  i.id, 
  i.contact, 
  i.comment, 
FROM invoice AS i
  LEFT JOIN contact ON i.contact = contact.id 
  LEFT JOIN line ON line.invoice = i.id
WHERE (
  contact.name LIKE '%SEARCH_TERM%' OR 
  i.comment LIKE '%SEARCH_TERM%' OR 
  line.designation LIKE '%SEARCH_TERM%'
)

查询多个表，但只从一个表中获取结果而不重复

3 个答案: