Let's say that we create the following table:
假设我们创建了下表:
CREATE TABLE example (
a integer,
b integer,
c integer,
PRIMARY KEY (a, c)
);
Obviously the compination of a and c has to be unique. But do a and c have to be unique themselves?
显然,a和c的组合必须是唯一的。但是a和c必须自己独一无二吗?
1 个解决方案
#1
3
No they don't have to be unique separately. Only pairs should be unique.
不,他们不必单独独特。只有对应该是唯一的。
Example:
a, c
1, 3
2, 3
2, 1
2, 1 -- this will cause unique key violation
INSERT INTO example(a,b,c) VALUES (1,2,3),(2,2,3),(2,3,1);
#1
3
No they don't have to be unique separately. Only pairs should be unique.
不,他们不必单独独特。只有对应该是唯一的。
Example:
a, c
1, 3
2, 3
2, 1
2, 1 -- this will cause unique key violation
INSERT INTO example(a,b,c) VALUES (1,2,3),(2,2,3),(2,3,1);