右连接子查询中的Mysql Access主表 [英] Mysql access main table inside right joined subquery
本文介绍了右连接子查询中的Mysql Access主表的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
SELECT id,region FROM ads
RIGHT JOIN (SELECT * FROM ads a2 WHERE a2.region=ads.region LIMIT 4) AS regions
ON regions.id=ads.id
说"unknown column ads.region".如何访问主表列区域?
Says "unknown column ads.region". How to access main table column region?
我需要为每个区域获取4行
I need to fetch 4 rows for each region
推荐答案
使用:
SELECT a.id,
a.region
FROM ads a
RIGHT JOIN (SELECT t.*,
CASE
WHEN @region = t.region THEN @rownum := @rownum + 1
ELSE @rownum := 1
END as rank,
@region := t.region
FROM ADS t
JOIN (SELECT @rownum := 0, @region := 1) r
ORDER BY t.region) b ON b.id = a.id
AND b.region = a.region
AND b.rank <= 4
这篇关于右连接子查询中的Mysql Access主表的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文