限制 SQL JOIN [英] LIMITing an SQL JOIN

问题描述

我正在尝试限制以下 SQL 语句.

I am trying to limit the following SQL statement.

SELECT expense.*, transaction.* FROM expense
INNER JOIN transaction ON expense_id = transaction_expense_id

我想做的是限制父"行的数量.IE.如果我执行 LIMIT 1，我将只收到一项费用项目，但仍会收到与之相关的所有交易.

What I want to do, is limit the number of 'parent' rows. IE. if I do a LIMIT 1, I would receive only one expense item, but still get all transactions associated with it.

这将如何实现?

在这个阶段，如果我做 LIMIT 1，我得到一笔费用，只有一笔交易.

At this stage, if I do LIMIT 1, I get one expense, and only one transaction.

推荐答案

所以假设我们可以排除 user 表，它可以重写为:

So assuming we can exclude the user table, it could be rewritten as:

select * from expense, transaction where expense_id = transaction_expense_id

现在如果你想应用一个限制，你可以这样做:

Now if you want to apply a limit, you could do it like this:

select * from expense, transaction where expense_id = transaction_expense_id and 
  expense_id in (select expense_id from expense limit 1)

这会做你想要的吗?显然，您需要谨慎对待您的费用 ID 将返回的顺序，因此您可能希望使用 ORDER BY 任何内容.

Would that do what you wanted? Obviously you need to be cautious about what order your expense_ids are going to come back in, so you probably want to use ORDER BY whatever.

鉴于您在下面的评论中描述的 MySQL 限制，也许这会起作用:

Given the MySQL limitation described in your comment below, maybe this will work:

select * from (select id from expense order by WHATEVER limit 1) as t1, transaction where expense_id=transaction_expense_id;

本

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