MySQL SQL First() 函数
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SQL First() Function
提问by gmustudent
I am using phpMyAdmin to write some SQL code that I thought was simple but proving to be a headache. I'm using thistutorial to help me out. My goal is to get the first and last columns id's from a result set. When I do this query I get 5 rows starting at 15 and going through 11.
我正在使用 phpMyAdmin 编写一些我认为很简单但事实证明很头疼的 SQL 代码。我正在使用本教程来帮助我。我的目标是从结果集中获取第一列和最后一列 id。当我执行此查询时，我得到 5 行，从 15 开始到 11。
SELECT id
FROM boardPost
WHERE recipientId = 1
ORDER BY id DESC
LIMIT 0,5
However, when I try this query I get an error #1064: "You have an error in your SQL syntax."
但是，当我尝试此查询时，我收到错误 #1064：“您的 SQL 语法有错误。”
SELECT FIRST(id)
FROM boardPost
WHERE recipientId = 1
ORDER BY id DESC
LIMIT 0,5
采纳答案by a_horse_with_no_name
Something like this maybe?
也许像这样的东西？
SELECT min(id), max(id)
from (
select id
from boardPost
where recipientId = 1
order by id desc
limit 0,5
) t
回答by Guido Hendriks
If you just want the first and the last idof a result set, you could consider this:
如果您只想要id结果集的第一个和最后一个，您可以考虑：
SELECT MIN(id) firstId, MAX(id) lastId FROM someTable WHERE aField = 1;
Note that it'll only work if you do use and ORDER BYan AUTO_INCREMENTfield, else you might get unexpected results.
请注意，如果你使用它只会工作，并ORDER BY在AUTO_INCREMENT现场，否则你可能会得到意想不到的效果。
It'll only work with the full set. If you need the first and last idof a limited one, you're probably better of using 2 queries with ASCand DESCorder and LIMIT 1.
它只适用于全套。如果您需要id有限的第一个和最后一个，您可能最好使用 2 个查询ASC和DESCorder 和LIMIT 1。
回答by John Conde
MySQL does not support the FIRST()function. You will need to use the workaround they specified in that tutorial (using ORDER BYand LIMIT)
MySQL 不支持该FIRST()功能。您将需要使用他们在该教程中指定的解决方法（使用ORDER BY和LIMIT）
回答by diego10
I think that is what you want?
我想这就是你想要的？
Select id from boardPost order by id asc limit 1
and
和
Select id from boardPost order by id desc limit 1
回答by ashleedawg
In some situations (like mine, that first brought me here), there are some rarely-used MySQL "windowing functions"such as FIRST_VALUEand LAST_VALUEthat may provide the functionality you're seeking.
在某些情况下（比如我的，第一次把我带到这里），有一些很少使用的 MySQL “窗口函数”，例如FIRST_VALUE和LAST_VALUE可能提供您正在寻找的功能。
(Here's more info on Window Function Concepts and Syntax, and the Wikipedia descriptionof the term.)
（这里有更多关于Window Function Concepts and Syntax 的信息，以及该术语的维基百科描述。）
