sql - 优化更新查询

Question

我正在寻找优化此查询的建议，该查询已经运行了一个多小时，其中表中包含约300,000行。我们使用的报告工具要求数据在被拉出时必须处于这种形状，因此重新设计表结构不是一种选择。该表如下所示：

CREATE TABLE [datatable](
    [RowID] [int] IDENTITY(1,1) NOT NULL,
    [CampaignID] [int] NOT NULL,
    [CampaignName] [nvarchar](255) NULL,
    [Category] [nvarchar](255) NOT NULL,
    [PostID] [int] NOT NULL,
    [TopicName] [nvarchar](4000) NULL,
    [TopicFrequency] [int] NULL
)

数据不断添加到表中，因此我必须定期更新主题频率。这是我当前的查询：

UPDATE  datatable
SET     TopicFrequency = b.TopicFrequency
FROM    datatable INNER JOIN
  (SELECT CampaignID, Category, TopicName, COUNT(DISTINCT PostID) AS TopicFrequency
    FROM datatable GROUP BY CampaignID, Category, TopicName) AS b 
    ON datatable.CampaignID = b.CampaignID 
    AND datatable.Category = b.Category 
    AND datatable.TopicName = b.TopicName

主题名称为nvarchar 4000，我无法在该字段上创建索引。寻找想法。谢谢。

Answer 1

一般决策-将表拆分为两个或多个表-即-标准化数据结构。我认为可以再引入两个表格-用于广告系列和主题

但

对于您当前的数据结构，您可以创建一个uniqueidentifier或bigint计算列作为TopicName字段的哈希，对其进行索引并查找哈希而不是字符串字段。我将为您提供bigint的示例：

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION [dbo].[HashString64SVF](@input NVARCHAR(4000))
RETURNS BIGINT
WITH SCHEMABINDING, RETURNS NULL ON NULL INPUT 
AS 
BEGIN
    RETURN
        CAST(SUBSTRING(HASHBYTES('SHA1', UPPER(@Input)), 1, 8) AS BIGINT) 
    ^   CAST(SUBSTRING(HASHBYTES('SHA1', UPPER(@Input)), 9, 8) AS BIGINT) 
    ^   CAST(SUBSTRING(HASHBYTES('SHA1', UPPER(@Input)), 17, 4) AS BIGINT) 
END
GO
ALTER TABLE datatable ADD TopicNameHash AS dbo.HashString64SVF(TopicName)
GO
CREATE INDEX NewIndexName ON DataTable(TopicNameHash, CampaignID, Category) INCLUDE(PostId)
GO
UPDATE  datatable
SET     TopicFrequency = b.TopicFrequency
FROM    datatable 
JOIN
  (SELECT CampaignID, Category, TopicNameHash, COUNT(DISTINCT PostID) AS TopicFrequency
    FROM datatable GROUP BY CampaignID, Category, TopicNameHash) AS b 
    ON datatable.CampaignID = b.CampaignID 
    AND datatable.Category = b.Category 
    AND datatable.TopicNameHash = b.TopicNameHash

和

在RowId列上创建主键

和

像这样重新创建表：

CREATE TABLE [datatable](
    [RowID] [int] IDENTITY(1,1) PRIMARY KEY,
    [CampaignID] [int] NOT NULL,
    [Category] [nvarchar](255) NOT NULL,
    [PostID] [int] NOT NULL,
    --uncomment if needed [TopicNameHash] AS dbo.HashString64SVF(TopicName),
    [TopicFrequency] [int] NULL,
    [CampaignName] [nvarchar](255) NULL,
    [TopicName] [nvarchar](4000) NULL
)

主要原因-如果您的可为空的变量列位于列列表的末尾并且这些列中有许多NULL值-sql server可以在行中节省一些空间，因此-在IO中