如何在MySQL中强制执行复合唯一性？
您可以借助UNIQUE关键字在MySQL中强制执行复合唯一性。这是将UNIQUE关键字添加到表列的语法。
语法如下
CREATE TABLE yourTableName ( yourColumnName1 datatype, yourColumnName2 datatype, yourColumnName3 datatype, . . N UNIQUE yourConstarintName(yourColumnName2,yourColumnName3) );
为了理解上述概念，让我们创建一个包含一些列的表，并向表中添加唯一约束。创建表的查询如下
mysql> create table UniqueDemo -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(100), -> StudentAge int, -> StudentMarks int -> , -> UNIQUE age_NameConstraint(StudentName,StudentAge) -> );
您可以借助SHOW命令从表中显示约束名称。
语法如下
SHOW INDEX FROM yourTableName;
要显示表中的唯一约束，请使用以上语法。查询如下-
mysql> SHOW INDEX FROM UniqueDemo;
以下是输出
+------------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | +------------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | uniquedemo | 0 | PRIMARY | 1 | StudentId | A | 0 | NULL | NULL | | BTREE | | | YES | | uniquedemo | 0 | age_NameConstraint | 1 | StudentName | A | 0 | NULL | NULL | YES | BTREE | | | YES | | uniquedemo | 0 | age_NameConstraint | 2 | StudentAge | A | 0 | NULL | NULL | YES | BTREE | | | YES | +------------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ 3 rows in set (0.33 sec)