SQL中的整数长度(即十进制字符串的长度)

Question

快速版:以下是最好的,为什么？(或者,还有更好的方法):

SELECT FLOOR(LOG10(Number))+1 AS NumLength FROM Table
SELECT LEN(CONVERT(VARCHAR, Number)) AS NumLength FROM Table
SELECT LEN(CAST(Number AS VARCHAR(10))) AS NumLength FROM Table

更详细一点:
我希望找出最有效的机制来计算整数的字符串表示的长度(更具体地说,是一个自然数 - 总是> 0).

我正在使用MS SQL Server(2005).

我已经提出了上面的3种解决方案,所有这些解决方案似乎都运行良好.

我知道第三个版本可能存在非常大的整数问题,但是现在我们可以假设"数字"长度不超过9位十进制数.

更详细的说明:( 你不必阅读这一点来回答我的问题)
这个查询在事务处理环境中被大量使用.
到目前为止,我已经假设"数字"总是正好是6位数.
但是,现在我必须更新代码以支持4到9位数字.

此SQL是识别卡的卡方案的条件的一部分.

完整查询尝试在开始和结束范围内查找与卡号开头匹配的记录.

所以完整的SQL条件将是这样的:

WHERE 
-- Start and End match
((Start=End OR End=0) AND (Start=CAST(LEFT('<card number>', FLOOR(LOG10(Start))+1) AS BIGINT))) OR 

-- Start != End
-- >= Start
(Start<=CAST(LEFT('<card number>', FLOOR(LOG10(Start))+1) AS BIGINT) AND 
-- <= End
End>=CAST(LEFT('<card number>', FLOOR(LOG10(Start))+1) AS BIGINT))

注意:
我可以重新设计表以使用VARCHAR而不是INT.这将允许我使用"LEN(开始)"而不是"FLOOR(LOG10(开始))+ 1)"但是条件将具有更多的CAST.
我更愿意继续处理INT,因为数据库模式将保持不变,并且无论如何处理INT应该比VARCHAR更快.

如果我将字段更改为VARCHAR,我的条件可能是:

WHERE 
-- Start and End match
((Start=End OR LEN(End)=0) AND (Start=LEFT('<card number>', LEN(Start)))) OR 

-- Start != End
-- >= Start
(CAST(Start AS BIGINT)<=CAST(LEFT('<card number>', LEN(Start)) AS BIGINT) AND 
-- <= End
CAST(End AS BIGINT)>=CAST(LEFT('<card number>', LEN(Start)) AS BIGINT))

非常感谢任何帮助,
戴夫

Answer 1

在我的机器上，版本 2 和版本 3 的结果大致相同，并且击败了其他两个。

编辑：虽然我刚刚想到我最初的测试有点不公平，CASE因为按升序排列语句意味着只有 10 个可能的数字满足第一个条件并提前退出。我在下面添加了一个额外的测试。您也可以尝试嵌套CASE语句来进行二分搜索。

SET NOCOUNT ON
SET STATISTICS TIME ON

  PRINT 'Test 1';

   WITH E00(N) AS (SELECT 1 UNION ALL SELECT 1),
        E02(N) AS (SELECT 1 FROM E00 a, E00 b),
        E04(N) AS (SELECT 1 FROM E02 a, E02 b),
        E08(N) AS (SELECT 1 FROM E04 a, E04 b),
        E16(N) AS (SELECT 1 FROM E08 a, E08 b),
        E32(N) AS (SELECT 1 FROM E16 a, E16 b),
   cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY N) FROM E32)
 SELECT MAX(FLOOR(LOG10(N))+1)
   FROM cteTally
  WHERE N <= 10000000;

  PRINT 'Test 2';

     WITH E00(N) AS (SELECT 1 UNION ALL SELECT 1),
        E02(N) AS (SELECT 1 FROM E00 a, E00 b),
        E04(N) AS (SELECT 1 FROM E02 a, E02 b),
        E08(N) AS (SELECT 1 FROM E04 a, E04 b),
        E16(N) AS (SELECT 1 FROM E08 a, E08 b),
        E32(N) AS (SELECT 1 FROM E16 a, E16 b),
   cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY N) FROM E32)
 SELECT MAX(LEN(CONVERT(VARCHAR, N)))
   FROM cteTally
  WHERE N <= 10000000;


  PRINT 'Test 3';

     WITH E00(N) AS (SELECT 1 UNION ALL SELECT 1),
        E02(N) AS (SELECT 1 FROM E00 a, E00 b),
        E04(N) AS (SELECT 1 FROM E02 a, E02 b),
        E08(N) AS (SELECT 1 FROM E04 a, E04 b),
        E16(N) AS (SELECT 1 FROM E08 a, E08 b),
        E32(N) AS (SELECT 1 FROM E16 a, E16 b),
   cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY N) FROM E32)
 SELECT MAX(LEN(CAST(N AS VARCHAR(10))))
   FROM cteTally
  WHERE N <= 10000000;

  PRINT 'Test 4';

     WITH E00(N) AS (SELECT 1 UNION ALL SELECT 1),
        E02(N) AS (SELECT 1 FROM E00 a, E00 b),
        E04(N) AS (SELECT 1 FROM E02 a, E02 b),
        E08(N) AS (SELECT 1 FROM E04 a, E04 b),
        E16(N) AS (SELECT 1 FROM E08 a, E08 b),
        E32(N) AS (SELECT 1 FROM E16 a, E16 b),
   cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY N) FROM E32)
SELECT MAX(CASE
             WHEN N < 10 THEN 1
             WHEN N < 100 THEN 2
             WHEN N < 1000 THEN 3
             WHEN N < 10000 THEN 4
             WHEN N < 100000 THEN 5
             WHEN N < 1000000 THEN 6
             WHEN N < 10000000 THEN 7
             WHEN N < 100000000 THEN 8
           END)
FROM   cteTally
WHERE  N <= 10000000;   

  PRINT 'Test 5';

     WITH E00(N) AS (SELECT 1 UNION ALL SELECT 1),
        E02(N) AS (SELECT 1 FROM E00 a, E00 b),
        E04(N) AS (SELECT 1 FROM E02 a, E02 b),
        E08(N) AS (SELECT 1 FROM E04 a, E04 b),
        E16(N) AS (SELECT 1 FROM E08 a, E08 b),
        E32(N) AS (SELECT 1 FROM E16 a, E16 b),
   cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY N) FROM E32)
 SELECT MAX(CASE 
             WHEN N >= 100000000 THEN NULL
             WHEN N >= 10000000 THEN 8
             WHEN N >= 1000000  THEN 7
             WHEN N >= 100000   THEN 6
             WHEN N >= 10000    THEN 5
             WHEN N >= 1000     THEN 4
             WHEN N >= 100      THEN 3
             WHEN N >= 10       THEN 2   
             ELSE                    1
            END   )
   FROM cteTally
  WHERE N <= 10000000;

在我的机器上运行的示例的结果是

Test 1
   CPU time = 9422 ms,  elapsed time = 9523 ms.

Test 2
   CPU time = 7021 ms,  elapsed time = 7130 ms.

Test 3
   CPU time = 6864 ms,  elapsed time = 7006 ms.

Test 4
   CPU time = 9328 ms,  elapsed time = 9456 ms.

Test 5
   CPU time = 6989 ms,  elapsed time = 7358 ms.