How do I implement stack in PL/SQL? - plsql

Question

In Python it would look something like this:
class Stack:
def __init__(self):
self.items = []
def isEmpty(self):
return self.items == []
def push(self, item):
self.items.append(item)
def pop(self):
return self.items.pop()
def peek(self):
return self.items[len(self.items)-1]
def size(self):
return len(self.items)
Which data structure do I use and how do I implement stack in Oracle PL/SQL?

Answer 1

You can achieve the object oriented kind of things by using OBJECT types.
Like a class in other programming languages, you can use OBJECT in PL/SQL for encapsulating data.
For example the stack definition: (lifted from ORACLE documentation link.... posted down below. You can find definition of below declaration in that link).
CREATE TYPE Stack AS OBJECT (
max_size INTEGER,
top INTEGER,
position IntArray,
MEMBER PROCEDURE initialize,
MEMBER FUNCTION full RETURN BOOLEAN,
MEMBER FUNCTION empty RETURN BOOLEAN,
MEMBER PROCEDURE push (n IN INTEGER),
MEMBER PROCEDURE pop (n OUT INTEGER)
);
https://docs.oracle.com/cd/A97630_01/appdev.920/a96624/13_elems32.htm

Answer 2

You can implement stacks in pl/sql using Associative array tables.
Consider the following example.
You can read more at the following locations:
Oracle Collections Documentation
Collections Tutorial
declare
type stack_type is table of binary_integer index by binary_integer;
---^ Use your data type here
stack stack_type;
procedure push( p_element in binary_integer ) as
-----^ Use your data type here
begin
stack( stack.count + 1 ) := p_element;
end push;
procedure pop as
begin
stack.delete( stack.count ) ;
end;
function find ( p_element in binary_integer )
-----^ Use your data type here
return boolean as
begin
for element in 1 .. stack.count loop
if stack( element ) = p_element then
return true;
end if;
end loop;
return false;
end;
function top
return binary_integer as
-------^ Use your data type here
begin
return stack( stack.count );
end;
begin
push( 123 );
push( 456 );
push( 678 );
push( 929 );
push( 104 );
for element in 1 .. stack.count loop
dbms_output.put_line( 'Element:' || element || ' Value: ' || stack( element ) );
end loop;
dbms_output.put_line( 'Find|Top:' || top() );
if find( 929 ) then
dbms_output.put_line( '929 Found' );
else
dbms_output.put_line( '929 Not found');
end if;
if find(321) then
dbms_output.put_line( '321 Found' );
else
dbms_output.put_line( '321 Not found');
end if;
while stack.count > 0 loop
dbms_output.put_line( 'Pop|Top:' || top() );
pop();
end loop;
end;