Thoughts on joint primary key

Yesterday, colleagues conducted service joint commissioning in the test environment , Suddenly, the maintenance information interface reports

Duplicate entry 'a-b-c' for key 'PRIMA

The first reaction is the problem of duplicate primary keys , A closer look at the table reveals , The union primary key used by this table (a,b,c), Let's look at the implementation SQL, Find out where After the condition a='xxx' and b='xxx', Immediately react , The unique identification of the data is a-b-c Determined by three field data , If use a-b To judge , Multiple pieces of data will be updated , And the final result is that multiple pieces of data become a-b-1 This situation , It definitely violates uniqueness .

resolvent ：

stay where a='xxx' and b='xxx' increase and c='xxx', Then execute the statement , Successfully solve the problem . Of course, there are careful questions , However, it also shows that colleagues do not fully understand the concept of joint primary key .