magic sh explain 11 Релизовать на основе одной таблицы стек для целочи

$ ./magic.sh explain 11
Релизовать на основе одной таблицы стек для целочисленных значений,
ограниченный глубиной 10, с функциями pop, push, top, clear.

CREATE OR REPLACE FUNCTION stack_clear() RETURNS void LANGUAGE 'SQL'
AS '
  DELETE FROM stack;
  INSERT INTO stack VALUES(0, 0);
';
CREATE OR REPLACE FUNCTION stack_top()
RETURNS INTEGER LANGUAGE 'SQL'
AS'
  SELECT val FROM stack WHERE id != 0 ORDER BY id DESC LIMIT 1;
';
CREATE OR REPLACE FUNCTION stack_push(INTEGER)
RETURNS INTEGER LANGUAGE 'SQL'
AS'
  INSERT INTO stack VALUES((SELECT MAX(id) + 1 FROM stack), $1);
  UPDATE stack SET val = (SELECT COUNT(id) - 1 FROM stack) WHERE id = 0; -- count without 0th record 
  DELETE FROM stack WHERE id > 10;
  SELECT (CASE WHEN val > 10 THEN 0 ELSE 1 END) FROM stack WHERE id = 0;
';
CREATE OR REPLACE FUNCTION stack_pop()
RETURNS INTEGER LANGUAGE 'SQL'
AS'
  UPDATE STACK SET val = (SELECT val FROM stack WHERE id > 0 ORDER BY id DESC LIMIT 1) WHERE id = 0;
  DELETE FROM stack WHERE id IN(SELECT id FROM stack WHERE id > 0 ORDER BY id DESC LIMIT 1);
  SELECT val FROM stack WHERE id = 0;
';
SELECT stack_clear();
 stack_clear 
-------------
 

SELECT stack_push(111), stack_push(222), stack_push(333);
 stack_push | stack_push | stack_push 
------------+------------+------------
          1 |          1 |          1

SELECT * FROM stack;
 id | val 
----+-----
  1 | 111
  2 | 222
  3 | 333
  0 |   3

SELECT stack_top();
 stack_top 
-----------
       333

SELECT * FROM stack;
 id | val 
----+-----
  1 | 111
  2 | 222
  3 | 333
  0 |   3

SELECT stack_pop();
 stack_pop 
-----------
       333

SELECT * FROM stack;
 id | val 
----+-----
  1 | 111
  2 | 222
  0 | 333

SELECT stack_pop();
 stack_pop 
-----------
       222

SELECT stack_pop();
 stack_pop 
-----------
       111

SELECT stack_pop();
 stack_pop 
-----------
          

SELECT * FROM stack;
 id | val 
----+-----
  0 |    

SELECT stack_clear();
 stack_clear 
-------------
 

SELECT * FROM stack;
 id | val 
----+-----
  0 |   0