为什么要使用主键？ [英] Why use primary keys?

问题描述

除了标识表中的唯一列之外，还使用哪些主键？不能仅通过在列上使用自动增量约束来完成此操作？我知道PK和FK用于关联不同的表，但是不能仅使用join来做到这一点吗？

What are primary keys used aside from identifying a unique column in a table? Couldn't this be done by simply using an autoincrement constraint on a column? I understand that PK and FK are used to relate different tables, but can't this be done by just using join?

使用主键加入数据库时​​，数据库在做什么以提高性能？

Basically what is the database doing to improve performance when joining using primary keys?

推荐答案

主要是为了使用外键实现引用完整性，当拥有PK时，它还会在后台创建索引，这样您在查找值时就无需进行表扫描

Mostly for referential integrity with foreign keys,, When you have a PK it will also create an index behind the scenes and this way you don't need table scans when looking up values

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