如何按列分组 - SQL 服务器

Question

我需要按 UniqueIdentifier 列分组，table 还包含 XML 列。

Table 架构：StudentMark:

CREATE TABLE [dbo].[StudentMark]
(
    [StudentMarkId] [int] IDENTITY(1,1) NOT NULL,
    [StudentId] [uniqueidentifier] NULL,
    [SubjectId] [uniqueidentifier] NULL,
    [ScoreInfo] [xml] NULL,
    [GeneratedOn] [datetime2](2) NOT NULL,

    CONSTRAINT [PK_StudentMark] 
       PRIMARY KEY CLUSTERED ([StudentMarkId] ASC)
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

样本种子数据

INSERT INTO [dbo].[StudentMark] ([StudentId], [SubjectId], [ScoreInfo], GeneratedOn])
VALUES ('FC3CB475-B480-4129-9190-6DE880E2D581', '0D72F79E-FB48-4D3E-9906-B78A9D105081', '<StudentMarkAttribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"></StudentMarkAttribute>', '2017-08-10 10:20:15'),
       ('0F4EF48C-93E3-41AA-8295-F6B0E8D8C3A2', '0D72F79E-FB48-4D3E-9906-B78A9D105081', '<StudentMarkAttribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"></StudentMarkAttribute>', '2017-08-10 10:20:15'),
       ('0F4EF48C-93E3-41AA-8295-F6B0E8D8C3A2', 'AB172272-D2E9-49E1-8040-6117BB6743DB', '<StudentMarkAttribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"></StudentMarkAttribute>', '2017-08-16 09:06:20'),
       ('FC3CB475-B480-4129-9190-6DE880E2D581', 'AB172272-D2E9-49E1-8040-6117BB6743DB', '<StudentMarkAttribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"></StudentMarkAttribute>', '2017-08-16 09:06:20');

需求：我需要按[dbo].[StudentMark].[StudentId]分组，取最新记录

我尝试了以下 SQL 查询，但它导致了错误

SELECT 
    MAX([StudentMarkId]), [StudentId], [SubjectId], [ScoreInfo], [GeneratedOn]
FROM 
    [dbo].[StudentMark] 
GROUP BY 
    [StudentId]

错误：

Column 'dbo.StudentMark.SubjectId' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

我参考了以下问题，但无法解决：Reason for Column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause

请帮助我。

Answer 1

使用ROW_NUMBER计算组内位置：

SELECT *
FROM (
    SELECT *,
      ROW_NUMBER() OVER(PARTITION BY StudentId ORDER BY StudentMarkId DESC) AS rn
    FROM [dbo].[StudentMark]) sub
WHERE sub.rn = 1;

Answer 2

如果您有 Students table:

，则替代解决方案效果最佳

select sm.*
from students s cross apply
     (select top 1 sm.*
      from studentmark sm
      where sm.studentid = s.studentid
      order by sm.generatedon desc
     ) sm;

Answer 3

您不能按 XML 或 TEXT 列分组，您首先需要转换为 varchar(max):

SELECT 
    MAX([StudentMarkId]), [StudentId], [SubjectId],
    CONVERT(XML, CONVERT(VARCHAR(MAX), [ScoreInfo])) DetailXML,
    [GeneratedOn]
FROM 
    [dbo].[StudentMark] 
GROUP BY 
    [StudentId], [SubjectId], 
    CONVERT(VARCHAR(MAX), [ScoreInfo]), [GeneratedOn]

第一行转换成varchar(max)来匹配GROUP BY子句，后面又转回XML.

如何按列分组 - SQL 服务器

How to Group By a column - SQL Server

xml

sql

sql-server

group-by

sql-server-2016