SQL Server：如何约束一个表以包含一行？ [英] SQL Server: how to constrain a table to contain a single row?

问题描述

我想在应用程序的配置表中存储一行。我想强制这个表只能包含一行。

I want to store a single row in a configuration table for my application. I would like to enforce that this table can contain only one row.

执行单行约束的最简单方法是什么？

What is the simplest way to enforce the single row constraint ?

推荐答案

p>您确保其中一列只能包含一个值，然后将其作为主键（或应用唯一性约束）。

You make sure one of the columns can only contain one value, and then make that the primary key (or apply a uniqueness constraint).

CREATE TABLE T1(
    Lock char(1) not null,
    /* Other columns */,
    constraint PK_T1 PRIMARY KEY (Lock),
    constraint CK_T1_Locked CHECK (Lock='X')
)

我有很多这些表在各种数据库，主要用于存储配置。知道这个配置项应该是一个int，你只会从数据库中读取一个int。

I have a number of these tables in various databases, mostly for storing config. It's a lot nicer knowing that, if the config item should be an int, you'll only ever read an int from the DB.

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