Question

我在MS Access中有表（Product_Id，category priority，atribute1，atribute2 ...），我正在尝试进行查询，按类别对数据进行排序并按最高优先级排序。优先级可以为空，因此应该放在最后。例：表

1, 100, 2, atr1, atr2
2, 300,  , atr1, atr2
3, 100, 5, atr1, atr2
4, 200, 9, atr1, atr2
5, 100,  , atr1, atr2
6, 200, 1, atr1, atr2

查询中预期的结果：

6, 200, 1, atr1, atr2
4, 200, 9, atr1, atr2
1, 100, 2, atr1, atr2
3, 100, 5, atr1, atr2
5, 100,  , atr1, atr2
2, 300,  , atr1, atr2

Answer 1

在Jet SQL中，这可能适合：

SELECT t2.MinOfPriority, tn.Field2, Nz([tn.Field3],999) AS Priority, 
       tn.Field4, tn.Field5
FROM tn 
INNER JOIN (SELECT Min(Nz(tn.Field3,999)) AS MinOfPriority, tn.Field2
            FROM  tn GROUP BY tn.Field2) AS t2 ON tn.Field2 = t2.Field2
ORDER BY t2.MinOfPriority, tn.Field2, Nz([Field3],999);

Answer 2

最简单的解决方案（在某些情况下不一定是最好的）是在订购表达式中使用列号：

SELECT t2.MinOfPriority, 
       tn.Field2, 
       Nz([tn.Field3],999) AS Priority,        
       tn.Field4, 
       tn.Field5

ORDER BY 1,2,3

Answer 3

你需要对类别进行加权（我用一些适当大的值加权null）：

select  t1.* 
from    myTable t1 
join 
( 

    select  category, min(coalesce(priority, 1000)) weight
    from    myTable 
    group by category
) t2 
on t1. category = t2. category
order by t2.weight, coalesce(t1. priority, 1000)

Answer 4

据我所知，当使用显式ORDER BY时，Jet 总是将NULL分类到结果集的末尾。

请参阅：ADO Provider Properties and Settings

“NULL归类顺序：一个Long值（只读），指定Null值的整理（排序）。对于Microsoft Jet提供程序，值始终为4，表示空值在低端排序列表。“

属性NULL Collation Order对提供程序是只读的这一事实强烈建议Jet引擎只有一个NULL排序规则，并且很高兴为您提供所需的。

Answer 5

Apparently NZ（Value，ValueToReturnIfNull）可以在MS Access上用作ISNULL的替代品，所以......

SELECT a.*
FROM this_table AS a 
    INNER JOIN 
    (
        SELECT category,min(NZ(priority,999999)) as min_priority_in_cat 
        FROM this_table group by category
    ) AS b ON a.category = b.category
ORDER BY  b.min_priority_in_cat, a.category, NZ(a.priority,999999)

如何使用分组行排序SQL查询

5 个答案: