在复合键中搜索缺失或重复的值

Question

Let's say I have a table with a two-part composite key like the following:

Key1  Key2  
a     char1  
a     char2  
a     char3  
a     char4  
a     char5
b     char1 
etc.

I need to check if there is a value form Key1 with missing or duplicated corresponding values from Key2 (ie values from key1 without 5 specific values from key2). I'm new to sql, thanks in advance for help.

Answer 1

Sample data:

SQL> select * From test order by key1, key2;

KEY1 KEY2
---- ----
a    ch1
a    ch2
a    ch3
b    ch1
c    ch2
c    ch3

6 rows selected.

One option is to

• create a cross-join of all [KEY1, KEY2] combinations
• using MINUS set operator, find missing values in the source table

---

SQL> with
  2  -- distinct keys
  3  k1 as (select distinct key1 from test),
  4  k2 as (select distinct key2 from test),
  5  -- cross join makes all possible combinations
  6  cj as
  7    (select a.key1, b.key2
  8     from k1 a cross join k2 b
  9    )
 10  -- MINUS set operator returns missing key combinations
 11  select key1, key2 from cj
 12  minus
 13  select key1, key2 from test;

KEY1 KEY2
---- ----
b    ch2
b    ch3
c    ch1

SQL>