使用单个 Case When 逻辑更新多列 - SQL 服务器

Question

我需要创建以下 XML 自定义元素和使用硬编码数据的属性。

Table 架构：StudentMark:

CREATE TABLE [dbo].[StudentMark]
(
    [StudentMarkId] int IDENTITY(1,1) NOT NULL,
    [StudentId] uniqueidentifier NOT NULL,
    [SubjectId] uniqueidentifier NOT NULL,
    [Score] int NOT NULL,
    [GeneratedOn] datetime2(2) NOT NULL,
    [IsPass] bit NULL,
    [Result] varchar(100) NULL,
    CONSTRAINT [PK_StudentMark] 
       PRIMARY KEY CLUSTERED ([StudentMarkId] ASC)
) ON [PRIMARY]

样本种子数据

INSERT INTO [dbo].[StudentMark] ([StudentId], [SubjectId], [GeneratedOn], [Score])
VALUES ('FC3CB475-B480-4129-9190-6DE880E2D581', '0D72F79E-FB48-4D3E-9906-B78A9D105081', '2017-08-10 10:10:15', 95),
       ('0F4EF48C-93E3-41AA-8295-F6B0E8D8C3A2', '0D72F79E-FB48-4D3E-9906-B78A9D105081', '2017-08-10 10:10:15', 60),
       ('0F4EF48C-93E3-41AA-8295-F6B0E8D8C3A2', 'AB172272-D2E9-49E1-8040-6117BB6743DB', '2017-08-16 09:06:20', 25),
       ('FC3CB475-B480-4129-9190-6DE880E2D581', 'AB172272-D2E9-49E1-8040-6117BB6743DB', '2017-08-16 09:06:20', 45);

要求：我需要根据单一逻辑更新几列[IsPass]和[Result]。

查询 #1:

UPDATE SM
SET SM.[Result] = CASE WHEN SM.[Score] >= 75 THEN N'OUTSTANDING'
     WHEN SM.[Score] >= 60 AND [Score] < 75 THEN N'VERY GOOD'
     WHEN SM.[Score] >= 50 AND [Score] < 60 THEN N'GOOD'
     WHEN SM.[Score] >= 40 AND [Score] < 50 THEN N'AVERAGE'
     ELSE N'FAIL' END
FROM [dbo].[StudentMark] SM

查询 #2:

UPDATE SM
SET SM.[IsPass] = CASE WHEN SM.[Result] = N'FAIL' THEN 0 ELSE 1 END
FROM [dbo].[StudentMark] SM

How could I merge these two query in a single UPDATE Query without replicating the CASE WHEN.

请帮助我。

Answer 1

UPDATE SM
SET SM.[Result] = CASE WHEN SM.[Score] >= 75 THEN N'OUTSTANDING'
     WHEN SM.[Score] >= 60 AND [Score] < 75 THEN N'VERY GOOD'
     WHEN SM.[Score] >= 50 AND [Score] < 60 THEN N'GOOD'
     WHEN SM.[Score] >= 40 AND [Score] < 50 THEN N'AVERAGE'
     ELSE N'FAIL' END, SM.[IsPass] = CASE WHEN SM.[Score] < 40 THEN 0 ELSE 1 END
FROM [dbo].[StudentMark] SM

您可以通过添加 ,(comma)

轻松做到这一点

Answer 2

像这样：

WITH DataSource ([StudentMarkId], [Result]) AS
(
    SELECT [StudentMarkId]
          ,CASE WHEN SM.[Score] >= 75 THEN N'OUTSTANDING'
             WHEN SM.[Score] >= 60 AND [Score] < 75 THEN N'VERY GOOD'
             WHEN SM.[Score] >= 50 AND [Score] < 60 THEN N'GOOD'
             WHEN SM.[Score] >= 40 AND [Score] < 50 THEN N'AVERAGE'
            ELSE N'FAIL' END
    FROM [dbo].[StudentMark]
)
UPDATE [dbo].[StudentMark]
SET SM.[Result] = DS.[Result]
   ,SM.[IsPass] = CASE WHEN DS.[Result] = N'FAIL' THEN 0 ELSE 1 END
FROM [dbo].[StudentMark] SM
INNER JOIN DataSource DS
    ON SM.[StudentMarkId] = DS.[StudentMarkId];

Answer 3

您可以简单地重复逻辑：

UPDATE SM
    SET SM.[Result] = (CASE WHEN SM.[Score] >= 75 THEN N'OUTSTANDING'
                            WHEN SM.[Score] >= 60 THEN N'VERY GOOD'
                            WHEN SM.[Score] >= 50 THEN N'GOOD'
                            WHEN SM.[Score] >= 40 THEN N'AVERAGE'
                            ELSE N'FAIL'
                       END),
        SM.IsPass = (CASE WHEN SM.Score >= 40 THEN 1 ELSE 0 END)
    FROM [dbo].[StudentMark] SM;

注意：CASE 表达式保证按顺序求值，因此每行只需要比较一次。

不过，我要指出的是，一个更好的选择可能是放弃 IsPass 作为 table 中的一列，并使其成为一个计算列：

alter table [dbo].[StudentMark]
    add IsPass as (CASE WHEN Result <> N'FAIL' THEN 1 ELSE 0 END);

这样可以确保值始终正确。事实上，您可以对 Result 执行相同的操作，因此两者都会被计算出来。

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