我有一个包含记录的表,其中有一行名为 category
.我插入了太多文章,我只想从每个类别中选择两篇文章.
I have a table with records and it has a row called category
. I have inserted too many articles and I want to select only two articles from each category.
我试图做这样的事情:
我创建了一个视图:
CREATE VIEW limitrows AS
SELECT * FROM tbl_artikujt ORDER BY articleid DESC LIMIT 2
然后我创建了这个查询:
Then I created this query:
SELECT *
FROM tbl_artikujt
WHERE
artikullid IN
(
SELECT artikullid
FROM limitrows
ORDER BY category DESC
)
ORDER BY category DESC;
但这不起作用并且只给我两条记录?
But this is not working and is giving me only two records?
LIMIT 只停止语句返回的结果数.您正在寻找的通常称为分析/窗口/排名函数 - MySQL 不支持,但您可以使用变量进行模拟:
LIMIT only stops the number of results the statement returns. What you're looking for is generally called analytic/windowing/ranking functions - which MySQL doesn't support but you can emulate using variables:
SELECT x.*
FROM (SELECT t.*,
CASE
WHEN @category != t.category THEN @rownum := 1
ELSE @rownum := @rownum + 1
END AS rank,
@category := t.category AS var_category
FROM TBL_ARTIKUJT t
JOIN (SELECT @rownum := NULL, @category := '') r
ORDER BY t.category) x
WHERE x.rank <= 3
如果您不更改 SELECT x.*
,结果集将包括 rank
和 var_category
值 - 您将拥有如果不是这种情况,请指定您真正想要的列.
If you don't change SELECT x.*
, the result set will include the rank
and var_category
values - you'll have to specify the columns you really want if this isn't the case.
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