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This article mainly introduces "what is the difference between unique and primary key in mysql". In daily operation, I believe that many people have doubts about the difference between unique and primary key in mysql. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the question of "what is the difference between unique and primary key in mysql?" Next, please follow the editor to study!

1. The unique constraint ensures that there are no duplicate values in the column, and both unique and primary key constraints provide a guarantee for the uniqueness of a column of values.

2. Unique can appear multiple times per table, while primary key can only appear one.

Example

Mysql > create table user (name varchar, constraint name_un unique (name)); Query OK, 0 rows affected (0.07 sec) mysql > insert user values ("Zhang San"); Query OK, 1 row affected (0.02 sec) mysql > insert user values ("Zhang San"); ERROR 1062 (23000): Duplicate entry 'for key' user.name_un'mysql > alter table user drop index name_un;Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 mysql > insert user values ("Zhang San") Query OK, 1 row affected (0.02 sec) at this point, the study on "what's the difference between unique and primary key in mysql" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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