Android 如何对每列使用Rank（），并获取顶部和底部的3个值

您好，我发现很难实现Rank（）函数，下面是我的示例表

id     category   value   volume
1      product1     0.4     0.5 
2      product2     0.9     0.6  
3      product3     0.3     0.7
4      product4     0.19    0.59 

现在我想分别对“value”和“volume”列进行排名，并获得每列的前3名和后3名，我正在firefox浏览器sqlmanager中测试下面的代码。但这个查询不起作用

SELECT Value, RANK() 
OVER (ORDER BY Value DESC) AS xRank 
FROM (SELECT Value FROM product_achievment) WHERE xRank>=3;

感谢您的帮助

is not不支持

排名

您有四个不同的查询，必须

UNION

因此，以下查询将返回所需的行：

SELECT * FROM product_achievement ORDER BY value LIMIT 3
UNION
SELECT * FROM product_achievement ORDER BY value DESC LIMIT 3
UNION
SELECT * FROM product_achievement ORDER BY volume LIMIT 3
UNION
SELECT * FROM product_achievement ORDER BY volume DESC LIMIT 3;

排名的变通方法

：

如果您还需要排名信息，我建议创建一个带有排名的

视图

：

CREATE VIEW ranked_product_achievement AS
SELECT *,
(SELECT COUNT() FROM product_achievement WHERE value<=t.value) AS r_value_a,
(SELECT COUNT() FROM product_achievement WHERE value>=t.value) AS r_value_d,
(SELECT COUNT() FROM product_achievement WHERE volume<=t.volume) AS r_volume_a,
(SELECT COUNT() FROM product_achievement WHERE volume>=t.volume) AS r_volume_d
FROM product_achievement AS t;

SELECT id, category, value, volume, r_value_a, r_volume_a
FROM ranked_product_achievement
WHERE r_value_a<=3 OR r_value_d<=3 OR r_volume_a<=3 OR r_volume_d<=3;