When or Why to use a “SET DEFINE OFF” in Oracle Database

Question

I'm watching a Script in Oracle and I see something I don't recognize

REM INSERTING into database1."Users"
 SET DEFINE OFF;
Insert into database1."Users" ("id","right") values ('1','R');

I'm looking for documentation about "set define off" and it's literally writing "disable the parsing of commands to replace substitution variable with their values"

I don't really understand what they want to say.

Can anyone help me?

Answer 1

By default, SQL Plus treats '&' as a special character that begins a substitution string. This can cause problems when running scripts that happen to include '&' for other reasons:

SQL> insert into customers (customer_name) values ('Marks & Spencers Ltd');
Enter value for spencers: 
old   1: insert into customers (customer_name) values ('Marks & Spencers Ltd')
new   1: insert into customers (customer_name) values ('Marks  Ltd')

1 row created.

SQL> select customer_name from customers;

CUSTOMER_NAME
------------------------------
Marks  Ltd

If you know your script includes (or may include) data containing '&' characters, and you do not want the substitution behaviour as above, then use set define off to switch off the behaviour while running the script:

SQL> set define off
SQL> insert into customers (customer_name) values ('Marks & Spencers Ltd');

1 row created.

SQL> select customer_name from customers;

CUSTOMER_NAME
------------------------------
Marks & Spencers Ltd

You might want to add set define on at the end of the script to restore the default behaviour.

Answer 2

Here is the example:

SQL> set define off;
SQL> select * from dual where dummy='&var';

no rows selected

SQL> set define on
SQL> /
Enter value for var: X
old   1: select * from dual where dummy='&var'
new   1: select * from dual where dummy='X'

D
-
X

With set define off, it took a row with &var value, prompted a user to enter a value for it and replaced &var with the entered value (in this case, X).