The difference between primary key, unique key and key in MySQL index

primary key

• Can uniquely identify each row of data in the database
• The primary key must contain a unique value
• The default primary key index
• There can only be one primary key index in a table

unique key

• Establish a unique index, that is, each row of data under the index is not repeated, and is mainly established to prevent duplication of inserted data
• There can be multiple unique indexes in a table

key

• The simplest and common index is generally used to speed up the query, and the index is the same, in most cases it is used as a foreign key