Difference between & and &&

& - is used to create a temporary substitution variable that will prompt you for a value every time it is reffered.

Eg: SQL> SELECT sal FROM emp WHERE ename LIKE '&NAME';

Enter value for name: SCOTT
old 1: SELECT sal FROM emp WHERE ename LIKE '&NAME'
new 1: SELECT sal FROM emp WHERE ename LIKE 'SCOTT'

SAL
----------
3000

SQL> /


Enter value for name: SCOTT
old 1: SELECT sal FROM emp WHERE ename LIKE '&NAME'
new 1: SELECT sal FROM emp WHERE ename LIKE 'SCOTT'

SAL
----------
3000

&& - is used to create a permanent substitution variable. Once you have entered a value its value will used every time the variable is referenced.

Eg: SQL> SELECT sal FROM emp WHERE ename LIKE '&&NAME';

Enter value for name: SCOTT
old 1: SELECT sal FROM emp WHERE ename LIKE '&&NAME'
new 1: SELECT sal FROM emp WHERE ename LIKE 'SCOTT'

SAL
----------
3000

SQL> /

old 1: SELECT sal FROM emp WHERE ename LIKE '&&NAME'
new 1: SELECT sal FROM emp WHERE ename LIKE 'SCOTT'

SAL
----------
3000