Question

I need to define and generate primary key for 2 or more tables.

Tables hold same type of data but FOR Some BUSINESS RULES we have to make them separate say like

TableA = LOCAL_CUSTOMERS
TableB = INTERNATIONAL_CUSTOMERS

Both hold same columns like, CUSTOMER_ID C_NAME, CITY ….etc

While designing the Primary Key I want these keys to be a combination of
PREFIX and an auto generated number, as an auto increamented int PK will do.

for example, CUSTOMER_ID (PK) for the table “LOCAL_CUSTOMERS”

LOC1, LOC2, LOC3,…… LOC5000

and CUSTOMER_ID (PK) for the table “INTERNATIONAL_CUSTOMERS”

INT1, INT2, INT3,…… INT5000

WHERE LOC and INT are prefix for LOCAL , INTERNATIONAL.

we can set auto increment in “identity specification” by using int but how can i do this ?
Is it “Computed Column Specification” I need to set for the column ?

Thanks

Answer 1

You can definitely do this with a computed column.

Either, if you stick with your two tables, you could just simply add a single computed, persisted column like this:

ALTER TABLE Local_Customer
  ADD CustomerID AS 'LOC' + CAST(ID AS VARCHAR(7)) PERSISTED

ALTER TABLE International_Customer
  ADD CustomerID AS 'INT' + CAST(ID AS VARCHAR(7)) PERSISTED

If you decide to have a single table with a discrimator column, e.g. “IsDomestic” of type BIT, you could do a single computed column that will use “LOC” or “INT” as prefix, based on the value of the “IsDomestic” column:

ALTER TABLE Customer
  ADD CustomerID AS CASE IsDomestic WHEN 0 THEN 'INT' ELSE 'LOC' END + CAST(ID AS VARCHAR(7)) PERSISTED

Either way – your “ID” field of type INT IDENTITY will be automatically increased for each row, and the computed column will create a more human-readable “CustomerID” automagically, without any further effort on your part.