The logical operators AND, OR, and NOT operate according to the value returned by the truth table .
AND and OR are binary operators; NOT is a unary operator.

These operators let you compare one expression to another. They are used in conditional control statements and SQL data manipulation statements. The result is always TRUE, FALSE, or NULL.

Relational operators are =, !=, <, >, <=, and >=. They allow for arbitrary comparisons of complex expressions.

The IS NULL operator returns a boolean value TRUE if its operand is null or FALSE if it is not null. Comparisons involving nulls always yield NULL. For example,
IF value IS NULL THEN
END IF;

You can use the LIKE operator to compare a character value to a pattern. Case is significant. For example,
SELECT * FROM CUSTOMER WHERE FIRSTNAME LIKE ‘Am%’;

This operator tests whether a value lies within a specified range. For example,
SELECT * FROM PRODUCT WHERE SALE_PRICE BETWEEN 40 AND 45;

The IN operator tests the existence of a value within a set of value. For example,
DELETE FROM CUSTOMER WHERE STATE IN ('FL', ‘NY’);

These operators let you manipulate strings by appending one string to another. For example,
SELECT * FROM PRODUCT WHERE PRODUCT_NAME = ‘F’ || ‘ish’;

PL/SQL supports the comparison of variables and constants in SQL and PL/SQL statements. These comparisons, called boolean expressions, generally consist of simple expressions separated by relational operators. Boolean expressions are often connected by logical operators NOT, AND, and OR. In PL/SQL, a boolean expression always evaluates to TRUE, FALSE, or NULL.

The operations within an expression are executed in a particular order depending on their precedence. Parentheses control the order of evaluation. The following table lists the order of operations.