Question

问题是此查询挂起或有无限记录，我不知道如何使用MS ACCESS修复：

预期的用户输入：

User input Start Date: 1/15/2015
User input End Date: 11/15/2015
User input Upper Data Threshold in kB: 50

来源表：

[Master] Table in Access:
Invc Date  Mobile Nbr     PktDtVol   
---------  ----------     --------   
1/15/15   647-409-8206    48kB
2/15/15   647-409-8206    33kB
3/15/15   647-409-8206    8000kB
4/15/15   647-409-8206    20kB
5/15/15   647-409-8206    10kB
6/15/15   647-409-8206    0kB
7/15/15   718-500-2311    3kB
8/15/15   718-500-2311    45kB
9/15/15   718-500-2311    25kB
10/15/15  514-300-3311    33kB
11/15/15  514-300-3311    20kB

[Temp_Table]中的输出：

Invc Date  Mobile Nbr     PktDtVol    Difference in Days 
---------  ----------     --------   -------------------
7/15/15    718-500-2311    3kB             304
8/15/15    718-500-2311    45kB            304
9/15/15    718-500-2311    25kB            304
10/15/15   514-300-3311    33kB            304
11/15/15   514-300-3311    20kB            304

接受SQL解决方案以生成上述输出：

PARAMETERS [Start Date] DateTime, [End Date] DateTime, [Upper Bound Usage in KB] IEEEDouble; 
SELECT m.[Invc Date], m.PktDtVol, m.[Mobile Nbr], DateDiff("d",[Start Date],[End Date]) AS [Difference in days] 
INTO Temp_Table FROM Master AS m 
WHERE (m.[Invc Date]>=[Start Date] And m.[Invc Date])<=[End Date] AND m.[Mobile Nbr] NOT IN 
(SELECT q.[Mobile Nbr] FROM Master AS q WHERE (q.PktDtVol>=[Upper Bound Usage in KB]));

从这里开始，我尝试通过另一个SQL语句修改表来创建索引来优化查询，但不起作用：

 CREATE INDEX Index2 ON Master([Ttl Charges])

查询工作正常，没有挂起源表中的10条记录，其中多条记录具有预期输出。但是当源表中有56,000条记录包含多条记录时，就会出现问题。

Answer 1

[Ttl Charges]的索引不会对你有任何帮助，但是[PktDtVol]上的索引会。我刚刚进行了10,000行测试，[PktDtVol]缺少索引肯定是性能瓶颈：

Indexes:
  none
Time:
  170 seconds (just under 3 minutes)

Indexes:
  [Invc Date]
  [Mobile Number]
Time:
  (same as before)

Indexes:
  [Invc Date]
  [Mobile Number]
  [PktDtVol]
Time:
  36 seconds

为了获得额外的性能提升，您可以重新构造查询以使用LEFT JOIN而不是带有子查询的NOT IN子句，如您在评论中所述：

PARAMETERS [Start Date] DateTime, [End Date] DateTime, [Upper Bound Usage in KB] IEEEDouble; 
SELECT 
    [Master].[Invc Date], 
    [Master].PktDtVol, 
    [Master].[Mobile Nbr], 
    DateDiff("d",[Start Date],[End Date]) AS [Difference in days] 
INTO Temp_Table 
FROM 
    [Master] 
    LEFT OUTER JOIN 
    (
        SELECT DISTINCT q.[Mobile Nbr] FROM Master AS q 
        WHERE (q.PktDtVol>=[Upper Bound Usage in KB])
    ) s 
        ON [Master].[Mobile Nbr] = s.[Mobile Nbr] 
WHERE 
    [Master].[Invc Date] >= [Start Date]
        AND [Master].[Invc Date] <= [End Date]
        AND s.[Mobile Nbr] IS NULL;

使用NOT IN子查询的SELECT INTO查询需要很长时间/挂起

1 个答案: