I'm trying to determine if a set of three columns on a table in Oracle would constitute a unique key and could be used in a 1:1 relationship.
我正在尝试确定Oracle中表上的一组三列是否构成唯一键，并且可以以1：1的关系使用。
If I run this query, and the keys are a unique combination, I should not see a count > 1, correct?
如果我运行此查询，并且键是唯一的组合，我不应该看到计数> 1，对吗？
select count(*) from my_table t
group by t.a, t.b, t.c
Is there a better/alternative way to make this determination?
是否有更好/替代的方法来做出这个决定？
2 个解决方案
#1
10
Use the HAVING clause to easily identify duplicates.
使用HAVING子句可以轻松识别重复项。
select t.a, t.b, t.c, count(1)
from my_table t
group by t.a, t.b, t.c
having count(1) > 1;
#2
0
If the table has a decent amount of data, it's probably easier to do
如果表具有相当数量的数据，则可能更容易
SELECT t.a, t.b, t.c, count(*)
FROM my_table t
GROUP BY t.a, t.b, t.c
HAVING COUNT(*) > 1
If that query returns 0 rows, the three columns are (currently) unique. If that query returns 1 or more rows, you'll know which values are duplicated.
如果该查询返回0行，则这三列（当前）是唯一的。如果该查询返回1行或更多行，您将知道哪些值是重复的。
Of course, if you find that the three columns are currently unique, you'll want to create a unique constraint if you intend to make use of that fact.
当然，如果您发现这三列当前是唯一的，那么如果您打算利用这一事实，则需要创建一个唯一约束。
#1
10
Use the HAVING clause to easily identify duplicates.
使用HAVING子句可以轻松识别重复项。
select t.a, t.b, t.c, count(1)
from my_table t
group by t.a, t.b, t.c
having count(1) > 1;
#2
0
If the table has a decent amount of data, it's probably easier to do
如果表具有相当数量的数据，则可能更容易
SELECT t.a, t.b, t.c, count(*)
FROM my_table t
GROUP BY t.a, t.b, t.c
HAVING COUNT(*) > 1
If that query returns 0 rows, the three columns are (currently) unique. If that query returns 1 or more rows, you'll know which values are duplicated.
如果该查询返回0行，则这三列（当前）是唯一的。如果该查询返回1行或更多行，您将知道哪些值是重复的。
Of course, if you find that the three columns are currently unique, you'll want to create a unique constraint if you intend to make use of that fact.
当然，如果您发现这三列当前是唯一的，那么如果您打算利用这一事实，则需要创建一个唯一约束。