OPERATOES IN PL/SQL:

a)  Logical        : AND,OR,NOT.
b)  Arithmetic        : +,-,*,/.
c)  Concatenation    : ||

  Parenthesis To Control Order of Operations

d) Exponentiation    : **
e) Comparison        : =,!=,<,>, <=,>=.
f) SQL*Plus         : IS NULL, LIKE, BETWEEN, IN.

PRECEDENCE:
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1) **,not
2) +,-(identity, Negation)
3) *,/
4) +,-
5) =,!=,<,>,<=,>=,IS NULL, LIKE, BETWEEN, IN.
6) AND
7) OR

OPERATORS IN PL/SQL, THINGS TO NOTE:

a) Comparison involving NULL's always yield NULL.
b) Applying logical operator NOT to a NULL yields NULL.
c) In Conditional Control Statements, if the condition yields NULL, its  associates sequence of statements are not executed.