Is there any difference between Rem and — comments for SQL*Plus?

Question

On SQL*Plus prompt, both Rem and -- qualify as comment indicators:

Rem this is a comment
-- this is also a comment
create table emp (
id number primary key,
name cvarchar2(40));

Is there any difference at all between the two commenting techniques?

Answer 1

The difference is that -- and /* */ can be used in a PL/SQL block, while REM[ARK] cannot. The following will work in SQL*Plus:

REM comment
-- comment
/* comment */
begin
   DBMS_OUTPUT.PUT_LINE('Test'); --comment
   DBMS_OUTPUT.PUT_LINE('Test'); /* comment */
end; 
/

These will not:

begin
   DBMS_OUTPUT.PUT_LINE('Test'); REM comment
end; 
/

begin
   REM comment
   DBMS_OUTPUT.PUT_LINE('Test');
end; 
/

The 11.2 documentation on all comment types has more comment information. The basics are...

You can enter comments in a script in three ways:

• using the SQL*Plus REMARK command for single line comments.

• using the SQL comment delimiters /*... */ for single or multi-line comments.

• using ANSI/ISO (American National Standards Institute/International Standards Organization) comments - - for single line comments.

The documentation also includes notes on four places that comments should not be used, but these do not include any further differences.

Answer 2

REM is supported due to being the way MS BATCH files are commented, and this tool being used with automation environments.

-- is supported due to being part of the SQL standard. ( http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt page 83 cf <comment introducer> ::= <minus sign><minus sign>[<minus sign>...] )

Answer 3

No there should be no difference at all.