Yes. This situation occurs in one-to-one relationships.
create table Table1 ( T1_Id integer not null primary key , T1_Data varchar(9) not null ) create table Table2 ( T2_Id integer not null primary key , T2_Data varchar(37) not null , foreign key (T2_Id) references Table1 (T1_Id) )
Why would someone design two tables like this? If it's a one-to-one relationship, couldn't you just include T2_Data in Table1? Yes, you could, although then you would also need to allow T2_Data to be NULL, if not every T1_Id has a matching T2_Id—in this case it's actually a one-to-zero-or-one relationship.
If it's a true one-to-one relationship, where every T1_Id has a matching T2_Id, then you could combine them without NULLs. Then the only reason why you might want separate tables would be if T2_Data were (a) infrequently queried, and (b) so large that it would result in many fewer physical rows on a physical database page, which would imply poorer performance for queries that used only T1_Data.
Dig Deeper on Oracle and SQL
Related Q&A from Rudy Limeback
Read SQL expert Rudy Limeback's advice for counting combinations in a table with SQL's GROUP BY clause Continue Reading
Read about the Mimer Validator, a tool used to verify your SQL code, in this tip from SQL expert Rudy Limeback. Continue Reading
Read an example of an SQL case expression from our SQL expert Rudy Limeback. Continue Reading