如何将自定义ID列与表的主键列同步

Question

Primarily, sorry for being too descriptive. I am storing patient's info in sql db by creating a custom ID field "PatientID" and I have a primary key field "ID". PatientID has a pattern "PID-1" or "PID-2" so on and so forth. I want to synchronize both IDs. Like if table's ID for "John" is 4 then its patientID should also be "PID-4". For this, I have done some coding like if no record exist then start saving patientID from "PID-1" and then for all next record first find the max id of patient from ID field and increment it by 1 and concatenate it with "PID" + (tableID+1).

 ID    PatientID
 1      PID-1
 2      PID-2
 3      PID-3
 4      PID-4

Now, for an instance, while adding more record an exception is thrown although record is not saved but ID gets incremented. And here comes the problem. Suppose, some bug comes and record for ID 5 could not be saved in the db, after fixing that bug when program runs correctly it put the ID 6 rather than 5. And for the patientID it puts "PID-5" due to MAX query. From here both IDs start being distinct. Same problem for deleting, if I am deleting last record from above table ie, 4 and PID-4, the next record's ID would be 5 while PatientID would be "PID-4". This was the whole problematic picture of handling both IDs from my side. Any alternate solution or any modification in my idea or any better idea then mine would be highly appreciated.

Answer 1

In SQL Server you could create a computed column for this purpose:

ALTER TABLE Patient DROP COLUMN PatientID;
GO
ALTER TABLE Patient ADD COLUMN PatientID AS ('PID-'+CAST(ID AS VARCHAR(15));

For more info regarding computed columns, please have a look here .

Note : I assumed that your table's name is Patient . You have to change this correspondingly if this is not the name of your table.