mysql约束条件unique是什么

-- 单列唯一，id列插入重复的数据就会报错

mysql> create table t(id int unique, name varchar(4));

Query OK, 0 rows affected (0.10 sec)

mysql> insert into t values(1, 'python'),(2, 'java');

Query OK, 2 rows affected, 1 warning (0.01 sec)

Records: 2  Duplicates: 0  Warnings: 1

mysql> insert into t values(1, 'python'),(2, 'java');

ERROR 1062 (23000): Duplicate entry '1' for key 'id'

-- 联合唯一，比如ip和port单个都可以重复，但是加起来必须是唯一的

mysql> create table t(id int unique, ip varchar(12), port varchar(4), unique(ip, port));

Query OK, 0 rows affected (0.01 sec)

mysql> insert into t values(1,'127.0.0.1',8080);

Query OK, 1 row affected (0.00 sec)

mysql> insert into t values(2,'127.0.0.1',8081);

Query OK, 1 row affected (0.00 sec)

mysql> insert into t values(3,'127.0.0.2',8080);

Query OK, 1 row affected (0.00 sec)

mysql> insert into t values(4,'127.0.0.1',8080);

ERROR 1062 (23000): Duplicate entry '127.0.0.1-8080' for key 'ip'