在MySQL中为重复键更新添加约束
要添加约束，语法如下：
alter table yourTableName add constraint anyName unique(yourColumnName);
让我们首先创建一个表-
mysql> create table DemoTable1459 -> ( -> Name varchar(20), -> Score int -> );
以下是为重复键更新添加约束的查询-
mysql> alter table DemoTable1459 add constraint Name_const unique(Name); Records: 0 Duplicates: 0 Warnings: 0
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1459 values('Chris',57) on duplicate key update Score=Score+10;
mysql> insert into DemoTable1459 values('David',89) on duplicate key update Score=Score+10;
mysql> insert into DemoTable1459 values('Chris',78) on duplicate key update Score=Score+10;使用select语句显示表中的所有记录-
mysql> select * from DemoTable1459;
这将产生以下输出-
+-------+-------+ | Name | Score | +-------+-------+ | Chris | 67 | | David | 89 | +-------+-------+ 2 rows in set (0.00 sec)