ALTER TABLE 添加复合主键

ALTER TABLE to add a composite primary key(ALTER TABLE 添加复合主键)

问题描述

我有一个名为 provider 的表.我有三列名为person、place、thing.可以有重复的人、重复的地点和重复的事物，但永远不可能有重复的人地物组合.

I have a table called provider. I have three columns called person, place, thing. There can be duplicate persons, duplicate places, and duplicate things, but there can never be a dupicate person-place-thing combination.

如何使用这三列在 MySQL 中为该表添加复合主键?

How would I ALTER TABLE to add a composite primary key for this table in MySQL with the these three columns?

推荐答案

ALTER TABLE provider ADD PRIMARY KEY(person,place,thing);

如果主键已经存在，那么你想这样做

If a primary key already exists then you want to do this

ALTER TABLE provider DROP PRIMARY KEY, ADD PRIMARY KEY(person, place, thing);

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