sql - 为什么我不能在同一个表上同时指定主键和唯一约束？

Question

我正在尝试创建一个表:

CREATE TABLE [MyTable]
(
    [Id] [int] IDENTITY,
    [Column1] [int] NOT NULL,
    [Column2] [int] NOT NULL

    CONSTRAINT [PK_MyTable_Id] PRIMARY KEY ([Id])
    CONSTRAINT [UQ_MyTable_Column1_Column2] UNIQUE ([Column1], [Column2])
)

此脚本失败并出现以下错误:

Both a PRIMARY KEY and UNIQUE constraint have been defined for column'Column2', table 'MyTable'. Only one is allowed.

为何实现此限制？如何创建具有这些属性的表？

Answer 1

主键约束后漏掉了一个逗号。

CREATE TABLE [MyTable]
(
    [Id] [int] IDENTITY,
    [Column1] [int] NOT NULL,
    [Column2] [int] NOT NULL

    CONSTRAINT [PK_MyTable_Id] PRIMARY KEY ([Id]),
    CONSTRAINT [UQ_MyTable_Column1_Column2] UNIQUE ([Column1], [Column2])
)