SQL Server:如何限制表包含单行?

SQL Server: how to constrain a table to contain a single row?(SQL Server:如何限制表包含单行?)

问题描述

我想在我的应用程序的配置表中存储一行.我想强制此表只能包含一行.

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.

强制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

您确保其中一列只能包含一个值，然后将其设为主键(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')
)

我在各种数据库中有许多这样的表，主要用于存储配置.知道如果配置项应该是 int 则更好，您将只会从 DB 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.

这篇关于SQL Server:如何限制表包含单行?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！