为什么这个查询需要这么长时间，我如何才能提高它的性能？

Question

我有一个查询，总而言之，将 N 相同的行插入到 table 中，唯一的区别是 1 列的值来自 0、1, ..., N 如果已经有一个具有该值的列，我不会插入 insert any 。我的程序是

BEGIN
    DECLARE @i INT = 0;
    WHILE(@i <= @boardPageCeiling)
    BEGIN
        IF NOT EXISTS(SELECT 1 FROM PageArchives WHERE PageType = 'Board' AND PageNum = @i)
        BEGIN
            INSERT INTO PageArchives
                (PageType, ThreadId, Html, PageNum, RetrievalAttempted, RetrievalSucceeded, RetrievalDate, RetrievalPriority, ProcessAttempted, ProcessingSucceeded, ProcessDate)
            VALUES
                ('Board', NULL, NULL, @i, 0, NULL, NULL, 0, 0, NULL, NULL)
        END
        SET @i = @i + 1;
    END
END

当 boardPageCeiling = 6000 时，执行时间超过 20 秒。考虑到复杂性，看起来特别长。

Answer 1

只需使用一个查询。唯一棘手的部分是生成一个数字序列：

WITH digits(d) as (
      SELECT *
      FROM (VALUES (0), (1), (2), (3), (4), (5), (6), (7), (8), (9)) v(d)
     ),
     n(n) as (
      SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) - 1 as seqnum
      FROM d CROSS JOIN d CROSS JOIN d CROSS JOIN d
     )
INSERT INTO PageArchives (PageType, PageNum, RetrievalDate, RetrievalPriority, ProcessAttempted)
    SELECT 'Board', PageNum, 0, 0, 0
    FROM n
    WHERE n.n <= @boardPageCeiling AND
          NOT EXISTS (SELECT 1 FROM PageArchives pa WHERE pa.PageNum = n.n);

我从 INSERT 中删除了 NULL 值，因为它们可能默认设置为 NULL。

Answer 2

您可以使用合并语句改进该查询

Answer 3

插入以下 table:

WITH NumberTable  AS (
  SELECT 1 as Number
  UNION ALL
  SELECT Number+1
  FROM NumberTable  
  WHERE Number < 100 
)
SELECT 'Board', NULL, NULL, Number, 0, NULL, NULL, 0, 0, NULL, NULL FROM NumberTable  
where Number not in (SELECT PageNum FROM PageArchives WHERE PageType = 'Board')
OPTION (MAXRECURSION 0);

只是一个示例查询，将“100”替换为您自己

为什么这个查询需要这么长时间，我如何才能提高它的性能？

Why does this query take so long, and how I can increase its performance?

sql

sql-server

stored-procedures

query-optimization

database-performance