如何避免 SQL 中 INSERT 的重复值? [英] How to avoid Duplicate values for INSERT in SQL?

问题描述

我有一张表:

Delegates

这个表有四个字段:

ID(Auto increment, Primary)
MemberNo, FromYr, ToYr

我用这个查询插入:

INSERT INTO Delegates ([MemNo],[FromYr],[ToYr]) values(@MemNo, @FromYr,@ToYr)

值来自用户输入.一个成员可以成为任何一年的代表，这就是为什么我允许他们随意输入.但现在的问题是他们可以错误地插入同一年的一个成员超过 2 次.请帮我现在在这里做什么?

The values comes from user input. One member can be a Delegate for any year that's why I allow them to input as they want. But now problem is they can insert mistakenly one member for the same year more than 2 times. Please help me what can I do now here?

推荐答案

插入前检查是否有相同值的记录:

Before inserting check if there is a record with the same values:

if not exists (select * from Delegates d where d.FromYr = @FromYr and d.MemNo = @MemNo)
    INSERT INTO Delegates ([MemNo],[FromYr],[ToYr]) values(@MemNo, @FromYr,@ToYr)

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