How to Use Operator Function in PL/SQL Database Management System But not in SQL

--Operator Function--

DECLARE  
message  varchar2(30):= ''That''s code4use.com!'';
BEGIN   dbms_output.put_line(message);
END;
--Arithmetic operator example
BEGIN
   dbms_output.put_line( 10 + 5);
   dbms_output.put_line( 10 - 5);
   dbms_output.put_line( 10 * 5);
   dbms_output.put_line( 10 / 5);
   dbms_output.put_line( 10 ** 5);
END;

--Relational operator example
DECLARE
   a number (2) := 21;
   b number (2) := 10;
BEGIN
   IF (a = b) then
      dbms_output.put_line('Line 1 - a is equal to b');
   ELSE
      dbms_output.put_line('Line 1 - a is not equal to b');
   END IF;

   IF (a < b) then
      dbms_output.put_line('Line 2 - a is less than b');
   ELSE
      dbms_output.put_line('Line 2 - a is not less than b');
   END IF;
  
   IF ( a > b ) THEN
      dbms_output.put_line('Line 3 - a is greater than b');
   ELSE
      dbms_output.put_line('Line 3 - a is not greater than b');
   END IF;

   -- Lets change value of a and b
   a := 5;
   b := 20;
   IF ( a <= b ) THEN
      dbms_output.put_line('Line 4 - a is either equal or less than b');
   END IF;

   IF ( b >= a ) THEN
      dbms_output.put_line('Line 5 - b is either equal or greater than a');
   END IF;
  
   IF ( a <> b ) THEN
      dbms_output.put_line('Line 6 - a is not equal to b');
   ELSE
      dbms_output.put_line('Line 6 - a is equal to b');
   END IF;

END;

--Conditional operator example
--Like operator
DECLARE
PROCEDURE compare (value  varchar2,  pattern varchar2 ) is
BEGIN
   IF value LIKE pattern THEN
      dbms_output.put_line ('True');
   ELSE
      dbms_output.put_line ('False');
   END IF;
END;

BEGIN
   compare('Zara Ali', 'Z%A_i');
   compare('Nuha Ali', 'Z%A_i');
END;

--Between operator
DECLARE
   x number(2) := 10;
BEGIN
   IF (x between 5 and 20) THEN
      dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;
  
   IF (x BETWEEN 5 AND 10) THEN
      dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;
  
   IF (x BETWEEN 11 AND 20) THEN
      dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;
END;

--In and Null operators
DECLARE
   letter varchar2(1) := 'm';
BEGIN
   IF (letter in ('a', 'b', 'c')) THEN
      dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;

   IF (letter in ('m', 'n', 'o')) THEN
       dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;
  
   IF (letter is null) THEN
    dbms_output.put_line('True');
   ELSE
      dbms_output.put_line('False');
   END IF;
END;

--Logical Operators
DECLARE
   a boolean := true;
   b boolean := false;
BEGIN
   IF (a AND b) THEN
      dbms_output.put_line('Line 1 - Condition is true');
   END IF;
   IF (a OR b) THEN
      dbms_output.put_line('Line 2 - Condition is true');
   END IF;
   IF (NOT a) THEN
      dbms_output.put_line('Line 3 - a is not true');
   ELSE
      dbms_output.put_line('Line 3 - a is true');
   END IF;
   IF (NOT b) THEN
      dbms_output.put_line('Line 4 - b is not true');
   ELSE
      dbms_output.put_line('Line 4 - b is true');
   END IF;
END;

--Operator precedence example
DECLARE
   a number(2) := 20;
   b number(2) := 10;
   c number(2) := 15;
   d number(2) := 5;
   e number(2) ;
BEGIN
   e := (a + b) * c / d;      -- ( 30 * 15 ) / 5
   dbms_output.put_line('Value of (a + b) * c / d is : '|| e );

   e := ((a + b) * c) / d;   -- (30 * 15 ) / 5
   dbms_output.put_line('Value of ((a + b) * c) / d is  : ' ||  e );

   e := (a + b) * (c / d);   -- (30) * (15/5)
   dbms_output.put_line('Value of (a + b) * (c / d) is  : '||  e );

   e := a + (b * c) / d;     --  20 + (150/5)
   dbms_output.put_line('Value of a + (b * c) / d is  : ' ||  e );
END;