Question

嗨，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

现在我想分别给列“值”和“音量”排名并获得每列的前3和后3，我在firefox浏览器sqlmanager中测试下面的代码。但查询无效。

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

感谢任何帮助。

Answer 1

sqlite不支持RANK。
您必须UNION有四个不同的查询。

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;

RANK的解决方法：

如果您还需要排名信息，我建议您创建一个排名为VIEW：

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;

然后你可以从创建的视图中SELECT：

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;

如何对每列使用Rank（）并获得top和bottom 3的值

1 个答案: