TRY_PARSE но быстрее - PullRequest
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TRY_PARSE но быстрее

0 голосов
/ 27 февраля 2019

Какой самый быстрый способ преобразования большого числа (почти 100) столбцов nvarchar в числа с плавающей точкой?

На данный момент у меня есть несколько операторов TRY_PARSE (имя-столбца AS FLOAT), по одному наcolumn.

Там, где столбец не разбирается, чтобы плавать, я хочу NULL.Нет уведомлений об ошибках, нет дополнительного интеллекта.

Есть ли более быстрый способ?Если это так, что бы это было?

SQL Server 2012

Ответы [ 2 ]

0 голосов
/ 27 февраля 2019

Шнуго сделал замечание, что TRY_CAST должно быть быстрее, поэтому я подумал, что лучше, чем тестировать, и из «быстрого» теста я согласен.

Во-первых, короткая настройкачтобы создать некоторые данные: 

USE Sandbox;
GO

DECLARE @SQL nvarchar(MAX);
CREATE TABLE TallyTable (I int);
WITH N AS(
    SELECT N
    FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)) N(N)),
Tally AS(
    SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
    FROM N N1
         CROSS JOIN N N2
         CROSS JOIN N N3)
INSERT INTO dbo.TallyTable (I)
SELECT I
FROM Tally;

SELECT @SQL =
       N'CREATE TABLE SampleTable (' + 
       STUFF((SELECT TOP 100
                     N',' + NCHAR(10) + 
                     N'    ' + QUOTENAME(CONCAT(N'Col',T.I)) + N' varchar(10)'
              FROM TallyTable T
              FOR XML PATH(N'')),1,1,N'') + NCHAR(10) + N');';
EXEC sp_executesql @SQL;
SELECT @SQL =
      N'INSERT INTO SampleTable' + NCHAR(10) + 
      N'VALUES(' + STUFF((SELECT TOP 100 ',0'
                          FROM TallyTable T
                          FOR XML PATH(N'')),1,1,N'') + N');';

EXEC sp_executesql @SQL;
GO

Это создает таблицу из 100 столбцов со значением «0».Теперь, если мы попробуем TRY_CAST и TRY_PARSE: 

SET STATISTICS TIME ON;

PRINT 'TRY_PARSE';

SELECT TRY_PARSE(Col1 AS float),
       TRY_PARSE(Col2 AS float),
       TRY_PARSE(Col3 AS float),
       TRY_PARSE(Col4 AS float),
       TRY_PARSE(Col5 AS float),
       TRY_PARSE(Col6 AS float),
       TRY_PARSE(Col7 AS float),
       TRY_PARSE(Col8 AS float),
       TRY_PARSE(Col9 AS float),
       TRY_PARSE(Col10 AS float),
       TRY_PARSE(Col11 AS float),
       TRY_PARSE(Col12 AS float),
       TRY_PARSE(Col13 AS float),
       TRY_PARSE(Col14 AS float),
       TRY_PARSE(Col15 AS float),
       TRY_PARSE(Col16 AS float),
       TRY_PARSE(Col17 AS float),
       TRY_PARSE(Col18 AS float),
       TRY_PARSE(Col19 AS float),
       TRY_PARSE(Col20 AS float),
       TRY_PARSE(Col21 AS float),
       TRY_PARSE(Col22 AS float),
       TRY_PARSE(Col23 AS float),
       TRY_PARSE(Col24 AS float),
       TRY_PARSE(Col25 AS float),
       TRY_PARSE(Col26 AS float),
       TRY_PARSE(Col27 AS float),
       TRY_PARSE(Col28 AS float),
       TRY_PARSE(Col29 AS float),
       TRY_PARSE(Col30 AS float),
       TRY_PARSE(Col31 AS float),
       TRY_PARSE(Col32 AS float),
       TRY_PARSE(Col33 AS float),
       TRY_PARSE(Col34 AS float),
       TRY_PARSE(Col35 AS float),
       TRY_PARSE(Col36 AS float),
       TRY_PARSE(Col37 AS float),
       TRY_PARSE(Col38 AS float),
       TRY_PARSE(Col39 AS float),
       TRY_PARSE(Col40 AS float),
       TRY_PARSE(Col41 AS float),
       TRY_PARSE(Col42 AS float),
       TRY_PARSE(Col43 AS float),
       TRY_PARSE(Col44 AS float),
       TRY_PARSE(Col45 AS float),
       TRY_PARSE(Col46 AS float),
       TRY_PARSE(Col47 AS float),
       TRY_PARSE(Col48 AS float),
       TRY_PARSE(Col49 AS float),
       TRY_PARSE(Col50 AS float),
       TRY_PARSE(Col51 AS float),
       TRY_PARSE(Col52 AS float),
       TRY_PARSE(Col53 AS float),
       TRY_PARSE(Col54 AS float),
       TRY_PARSE(Col55 AS float),
       TRY_PARSE(Col56 AS float),
       TRY_PARSE(Col57 AS float),
       TRY_PARSE(Col58 AS float),
       TRY_PARSE(Col59 AS float),
       TRY_PARSE(Col60 AS float),
       TRY_PARSE(Col61 AS float),
       TRY_PARSE(Col62 AS float),
       TRY_PARSE(Col63 AS float),
       TRY_PARSE(Col64 AS float),
       TRY_PARSE(Col65 AS float),
       TRY_PARSE(Col66 AS float),
       TRY_PARSE(Col67 AS float),
       TRY_PARSE(Col68 AS float),
       TRY_PARSE(Col69 AS float),
       TRY_PARSE(Col70 AS float),
       TRY_PARSE(Col71 AS float),
       TRY_PARSE(Col72 AS float),
       TRY_PARSE(Col73 AS float),
       TRY_PARSE(Col74 AS float),
       TRY_PARSE(Col75 AS float),
       TRY_PARSE(Col76 AS float),
       TRY_PARSE(Col77 AS float),
       TRY_PARSE(Col78 AS float),
       TRY_PARSE(Col79 AS float),
       TRY_PARSE(Col80 AS float),
       TRY_PARSE(Col81 AS float),
       TRY_PARSE(Col82 AS float),
       TRY_PARSE(Col83 AS float),
       TRY_PARSE(Col84 AS float),
       TRY_PARSE(Col85 AS float),
       TRY_PARSE(Col86 AS float),
       TRY_PARSE(Col87 AS float),
       TRY_PARSE(Col88 AS float),
       TRY_PARSE(Col89 AS float),
       TRY_PARSE(Col90 AS float),
       TRY_PARSE(Col91 AS float),
       TRY_PARSE(Col92 AS float),
       TRY_PARSE(Col93 AS float),
       TRY_PARSE(Col94 AS float),
       TRY_PARSE(Col95 AS float),
       TRY_PARSE(Col96 AS float),
       TRY_PARSE(Col97 AS float),
       TRY_PARSE(Col98 AS float),
       TRY_PARSE(Col99 AS float),
       TRY_PARSE(Col100 AS float)
FROM dbo.SampleTable;

PRINT 'TRY_CAST';

SELECT TRY_CAST(Col1 AS float),
       TRY_CAST(Col2 AS float),
       TRY_CAST(Col3 AS float),
       TRY_CAST(Col4 AS float),
       TRY_CAST(Col5 AS float),
       TRY_CAST(Col6 AS float),
       TRY_CAST(Col7 AS float),
       TRY_CAST(Col8 AS float),
       TRY_CAST(Col9 AS float),
       TRY_CAST(Col10 AS float),
       TRY_CAST(Col11 AS float),
       TRY_CAST(Col12 AS float),
       TRY_CAST(Col13 AS float),
       TRY_CAST(Col14 AS float),
       TRY_CAST(Col15 AS float),
       TRY_CAST(Col16 AS float),
       TRY_CAST(Col17 AS float),
       TRY_CAST(Col18 AS float),
       TRY_CAST(Col19 AS float),
       TRY_CAST(Col20 AS float),
       TRY_CAST(Col21 AS float),
       TRY_CAST(Col22 AS float),
       TRY_CAST(Col23 AS float),
       TRY_CAST(Col24 AS float),
       TRY_CAST(Col25 AS float),
       TRY_CAST(Col26 AS float),
       TRY_CAST(Col27 AS float),
       TRY_CAST(Col28 AS float),
       TRY_CAST(Col29 AS float),
       TRY_CAST(Col30 AS float),
       TRY_CAST(Col31 AS float),
       TRY_CAST(Col32 AS float),
       TRY_CAST(Col33 AS float),
       TRY_CAST(Col34 AS float),
       TRY_CAST(Col35 AS float),
       TRY_CAST(Col36 AS float),
       TRY_CAST(Col37 AS float),
       TRY_CAST(Col38 AS float),
       TRY_CAST(Col39 AS float),
       TRY_CAST(Col40 AS float),
       TRY_CAST(Col41 AS float),
       TRY_CAST(Col42 AS float),
       TRY_CAST(Col43 AS float),
       TRY_CAST(Col44 AS float),
       TRY_CAST(Col45 AS float),
       TRY_CAST(Col46 AS float),
       TRY_CAST(Col47 AS float),
       TRY_CAST(Col48 AS float),
       TRY_CAST(Col49 AS float),
       TRY_CAST(Col50 AS float),
       TRY_CAST(Col51 AS float),
       TRY_CAST(Col52 AS float),
       TRY_CAST(Col53 AS float),
       TRY_CAST(Col54 AS float),
       TRY_CAST(Col55 AS float),
       TRY_CAST(Col56 AS float),
       TRY_CAST(Col57 AS float),
       TRY_CAST(Col58 AS float),
       TRY_CAST(Col59 AS float),
       TRY_CAST(Col60 AS float),
       TRY_CAST(Col61 AS float),
       TRY_CAST(Col62 AS float),
       TRY_CAST(Col63 AS float),
       TRY_CAST(Col64 AS float),
       TRY_CAST(Col65 AS float),
       TRY_CAST(Col66 AS float),
       TRY_CAST(Col67 AS float),
       TRY_CAST(Col68 AS float),
       TRY_CAST(Col69 AS float),
       TRY_CAST(Col70 AS float),
       TRY_CAST(Col71 AS float),
       TRY_CAST(Col72 AS float),
       TRY_CAST(Col73 AS float),
       TRY_CAST(Col74 AS float),
       TRY_CAST(Col75 AS float),
       TRY_CAST(Col76 AS float),
       TRY_CAST(Col77 AS float),
       TRY_CAST(Col78 AS float),
       TRY_CAST(Col79 AS float),
       TRY_CAST(Col80 AS float),
       TRY_CAST(Col81 AS float),
       TRY_CAST(Col82 AS float),
       TRY_CAST(Col83 AS float),
       TRY_CAST(Col84 AS float),
       TRY_CAST(Col85 AS float),
       TRY_CAST(Col86 AS float),
       TRY_CAST(Col87 AS float),
       TRY_CAST(Col88 AS float),
       TRY_CAST(Col89 AS float),
       TRY_CAST(Col90 AS float),
       TRY_CAST(Col91 AS float),
       TRY_CAST(Col92 AS float),
       TRY_CAST(Col93 AS float),
       TRY_CAST(Col94 AS float),
       TRY_CAST(Col95 AS float),
       TRY_CAST(Col96 AS float),
       TRY_CAST(Col97 AS float),
       TRY_CAST(Col98 AS float),
       TRY_CAST(Col99 AS float),
       TRY_CAST(Col100 AS float)
FROM dbo.SampleTable;

SET STATISTICS TIME OFF;

Результаты выше незначительны, но все равно показывает: 

TRY_PARSE

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

(1 row affected)

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 4 ms.
TRY_CAST

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

(1 row affected)

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

Это 4ms отличается от 1ряд из 100 столбцов.Тогда давайте увеличим объем (это займет некоторое время): 

DECLARE @SQL nvarchar(MAX);
SELECT @SQL =
      N'INSERT INTO SampleTable' + NCHAR(10) + 
      N'VALUES' +STUFF((SELECT N',' + NCHAR(10) +
      N'       (' + STUFF((SELECT TOP 100 ',0'
                                              FROM TallyTable T
                                              FOR XML PATH(N'')),1,1,N'') + N')'
                        FROM TallyTable T
                        FOR XML PATH(N'')),1,1,N'') + N';';

SELECT @SQL;
EXEC sp_executesql @SQL;
EXEC sp_executesql @SQL;
EXEC sp_executesql @SQL;
EXEC sp_executesql @SQL;
EXEC sp_executesql @SQL;
--Now we have 5001 rows

Теперь у нас есть 5 001 строка и 100 столбцов.Теперь, если мы снова запустим описанное выше ... 

TRY_PARSE

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

(5001 rows affected)

 SQL Server Execution Times:
   CPU time = 14672 ms,  elapsed time = 18690 ms.
TRY_CAST

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

(5001 rows affected)

 SQL Server Execution Times:
   CPU time = 125 ms,  elapsed time = 671 ms.

Ошеломляющая разница в 18019 мс (это на 18 секунд или почти в 28 раз быстрее!).

Итак, ответ таков:используйте TRY_CAST (или TRY_CONVERT, что, я уверен, будет так же быстро). 

--cleanup
DROP TABLE dbo.TallyTable;
DROP TABLE SampleTable;
0 голосов
/ 27 февраля 2019

Просто короткий тест, чтобы показать разницу в производительности между TRY_PARSE и TRY_CAST

Мой результат

  • TRY_CAST 327 мс
  • TRY_PARSE 17784 мс

Это означает, что TRY_CAST примерно в 50 раз быстрее, чем TRY_PARSE (кстати: TRY_CONVERT почти совпадает с TRY_CAST по производительности).

Попробуйте и опубликуйте свои результаты; -) 

SET LANGUAGE ENGLISH;

DECLARE @tbl TABLE(SomeFloatAsString VARCHAR(100),fl2 VARCHAR(100),fl3 VARCHAR(100),fl4 VARCHAR(100),fl5 VARCHAR(100),fl6 VARCHAR(100),fl7 VARCHAR(100),fl8 VARCHAR(100),fl9 VARCHAR(100),fl10 VARCHAR(100));
DECLARE @i INT=0;
WHILE @i<100000
BEGIN
    INSERT INTO @tbl VALUES(RAND(),RAND(),RAND(),RAND(),RAND(),RAND(),RAND(),RAND(),RAND(),RAND());
    SET @i+=1;
END

DECLARE @d DATETIME2 = SYSUTCDATETIME();

SELECT TRY_CAST(SomeFloatAsString AS FLOAT) fl1
      ,TRY_CAST(fl2 AS FLOAT) fl2
      ,TRY_CAST(fl3 AS FLOAT) fl3
      ,TRY_CAST(fl4 AS FLOAT) fl4
      ,TRY_CAST(fl5 AS FLOAT) fl5
      ,TRY_CAST(fl6 AS FLOAT) fl6
      ,TRY_CAST(fl7 AS FLOAT) fl7
      ,TRY_CAST(fl8 AS FLOAT) fl8
      ,TRY_CAST(fl9 AS FLOAT) fl9
      ,TRY_CAST(fl10 AS FLOAT)fl10
INTO #tmp1
FROM @tbl

SELECT DATEDIFF(MILLISECOND,@d,SYSUTCDATETIME())


DECLARE @d2 DATETIME2 = SYSUTCDATETIME();

SELECT TRY_PARSE(SomeFloatAsString AS FLOAT) fl1
      ,TRY_PARSE(fl2 AS FLOAT) fl2 
      ,TRY_PARSE(fl3 AS FLOAT) fl3
      ,TRY_PARSE(fl4 AS FLOAT) fl4
      ,TRY_PARSE(fl5 AS FLOAT) fl5
      ,TRY_PARSE(fl6 AS FLOAT) fl6
      ,TRY_PARSE(fl7 AS FLOAT) fl7
      ,TRY_PARSE(fl8 AS FLOAT) fl8
      ,TRY_PARSE(fl9 AS FLOAT) fl9
      ,TRY_PARSE(fl10 AS FLOAT)fl10
INTO #tmp2
FROM @tbl

SELECT DATEDIFF(MILLISECOND,@d2,SYSUTCDATETIME());
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