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UNIQUE 指数如何在多个列上发挥作用?
原标题:How do UNIQUE indexes work on multiple columns?

如果我在email,password 列上添加 UNIQUE 索引,将会检查索引是否:

  1. Is email unique AND is password unique, or
  2. The combination of email,password is unique, as in, it would allow [email protected], 123 and [email protected], 123

对不起,如果我的想法在这里显得突然,我今天由于某种原因难以表达这些想法。

最佳回答

您的第二个答案是正确的。 两个字段的组合必须是独特的 。

对于 # 1, 您需要为每列单列单列单列的索引 。

问题回答

我同意@redFilter 的 组合是一个更好的选项。 但记住 UNIQUE 与主键不同。 您可以在 UNIQUE 中拥有无效值, 如果您想要避免在创建表格时在每个数据类型结尾处使用“ NOT NULL ” 。





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