如何检查一个值是否已经存在以避免重复? [英] How to check if a value already exists to avoid duplicates?

问题描述

我有一个URL表，并且我不需要任何重复的URL.如何使用PHP/MySQL检查表中是否已存在给定的URL?

I've got a table of URLs and I don't want any duplicate URLs. How do I check to see if a given URL is already in the table using PHP/MySQL?

推荐答案

如果您不想重复，可以执行以下操作:

If you don't want to have duplicates you can do following:

• 添加唯一性约束
• 使用"替换"或"在重复键更新上插入... 语法

• add uniqueness constraint
• use "REPLACE" or "INSERT ... ON DUPLICATE KEY UPDATE" syntax

如果多个用户可以将数据插入数据库，@ Jeremy Ruten建议的方法可能导致错误:执行检查后，某人可以将相似的数据插入表中.

If multiple users can insert data to DB, method suggested by @Jeremy Ruten, can lead to an error: after you performed a check someone can insert similar data to the table.

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