SQL查询以使用最大聚合选择行并将它们放在一起

Question

我有一个表，其中第一列是键值。 我必须为每个键值选择一行（选择具有最大“计数”字段的键值），然后将它们彼此相邻排列。 我为此编写了此查询：

SELECT name as "name",
MAX(CASE WHEN key_id=8 THEN count ELSE 0.0 END) AS "key_1",
key_value as "key_1_value",
MAX(CASE WHEN key_id=9 THEN count ELSE 0.0 END) AS "key_2",
key_value as "key_2_value",
MAX(CASE WHEN key_id=10 THEN count ELSE 0.0 END) AS "key_3",
key_value as "key_2_value"
FROM table1 GROUP BY  name;

我得到的结果是：

name1      281000018371    0.881841        247000421624    0.881841        285000032094    0.881841

计数的值是正确的，即该特定key_id的计数的最大值，但是key_value仅对于第一个key_id正确，对于其他两个重复。 有人可以告诉我如何更改此查询，以便从具有相应key_id和max（count）的行中获取key_value。

Answer 1

这是您要做什么？

SELECT 
    name as "name",
    MAX(CASE WHEN key_id=8 THEN count ELSE 0.0 END) AS "key_1",
    MAX(CASE WHEN key_id=8 THEN key_value END) AS "key_1_value",
    MAX(CASE WHEN key_id=9 THEN count ELSE 0.0 END) AS "key_2",
    MAX(CASE WHEN key_id=9 THEN key_value END) AS "key_2_value",
    MAX(CASE WHEN key_id=10 THEN count ELSE 0.0 END) AS "key_3",
    MAX(CASE WHEN key_id=10 THEN key_value END) AS "key_3_value"
FROM table1 
GROUP BY  name;

如果没有样本数据，我假设您正在查看多行，并尝试将某些键放入列中。 您的原始查询为每个列提取相同的值。

编辑：如果您有大量数据，性能对此将是可怕的 ，但是您可以尝试执行此操作...

SELECT 
    name as "name",
    MAX(CASE WHEN key_id=8 THEN count ELSE 0.0 END) AS "key_1",
    (SELECT TOP 1 key_value FROM Table1 k1 WHERE k1.name = Table1.name AND key_id = 8 ORDER BY Count DESC) as "key_1_value",
    MAX(CASE WHEN key_id=9 THEN count ELSE 0.0 END) AS "key_2",
    (SELECT TOP 1 key_value FROM Table1 k2 WHERE k2.name = Table1.name AND key_id = 9 ORDER BY Count DESC) as "key_2_value",
    MAX(CASE WHEN key_id=10 THEN count ELSE 0.0 END) AS "key_3",
    (SELECT TOP 1 key_value FROM Table1 k3 WHERE k3.name = Table1.name AND key_id = 10 ORDER BY Count DESC) as "key_3_value"
FROM table1 
GROUP BY  name;

Answer 2

嗯...也许：

SELECT distinct name, b.MaxCount, b.Key_Value, c.MaxCount, c.Key_Value, d.MaxCount, d.Key_Value
from table1 a
left join 
(SELECT key_Value, MAX(ifnull((count,0)) as MaxCount from table1 where key_id =8 group by key_Value) b
on a.name = b.name
left join 
(SELECT key_Value, MAX(ifnull((count,0)) as MaxCount from table1 where key_id =9 group by key_Value) c
on a.name = b.name
left join 
(SELECT key_Value, MAX(ifnull((count,0)) as MaxCount from table1 where key_id =10 group by key_Value) d
on a.name = b.name
group by name

我认为您的加入条件。

您遇到IO错误。 这可能是因为在SQLITE中，isnull应该为ifnull。 对此表示抱歉。