What is the difference between Oracle's VARCHAR and VARCHAR2 datatypes?

Question

When migrating tables coming from other DBMSs to Oracle, one of the standard tasks is to replace all VARCHAR(n) fields with VARCHAR2(n) fields (provided n <= 4000).

Why does Oracle call this datatype VARCHAR2 and not just VARCHAR like other DBMSs?

Answer 1

It would seem that Oracle at one time had plans to give a different definition to VARCHAR than to VARCHAR2. It has told customers this and recommends against using VARCHAR. Whatever their plans were, as of 11.2.0.2 VARCHAR is identical to VARCHAR2. Here is what the SQL Language Reference 11g Release 2 says:

Do not use the VARCHAR data type. Use the VARCHAR2 data type instead. Although the VARCHAR data type is currently synonymous with VARCHAR2, the VARCHAR data type is scheduled to be redefined as a separate data type used for variable-length character strings compared with different comparison semantics.

The PL/SQL User's Guide and Reference 10g Release 2 puts it this way:

Currently, VARCHAR is synonymous with VARCHAR2. However, in future releases of PL/SQL, to accommodate emerging SQL standards, VARCHAR might become a separate datatype with different comparison semantics. It is a good idea to use VARCHAR2 rather than VARCHAR.

The Database Concepts 10g Release 2 document says the same thing in stronger terms:

The VARCHAR datatype is synonymous with the VARCHAR2 datatype. To avoid possible changes in behavior, always use the VARCHAR2 datatype to store variable-length character strings.

The Oracle 9.2 and 8.1.7 documentation say essentially the same thing, so even though Oracle continually discourages the use of VARCHAR, so far they haven't done anything to change it's parity with VARCHAR2.

Answer 2

Currently, the two are synonymous.

VARCHAR is an ANSI standard data type but Oracle's implementation of the VARCHAR data type violates the ANSI standard by considering the empty string to be NULL (Oracle's implementation predates the ANSI standard). As Leigh points out, Oracle has stated that the semantics of the VARCHAR data type may change in the future with respect to how the empty string is treated. If and when that happens, the semantics of the VARCHAR2 data type will remain the same. Using the VARCHAR2 data type is safer because you don't have to worry that some future version of Oracle will break your code by causing empty strings to no longer be considered NULL.

Answer 3

Because in the original SQL standard a VARCHAR was 255 characters, and Oracle were at least having a stab at standards compliance in those days.