create table exams (
  sid integer,
  cid integer,
  score integer,
  PRIMARY KEY (sid, cid)
);

insert into exams values
(1, 1, 90),
-- (1, 2, 90),
-- (1, 3, 70),
-- (1, 4, 70),
(2, 1, 90),
(2, 2, 90),
(3, 1, 90)
;


SELECT sid, score from exams order by (sid, score) DESC;

CREATE OR REPLACE FUNCTION list_scnd_highest()
RETURNS TABLE (stu_id integer, scnd_score integer) as $$
DECLARE
    curs CURSOR FOR (SELECT sid, score from exams order by sid, score DESC);
    r1 RECORD;
    r2 RECORD;
    current_sid integer;
    
BEGIN
    OPEN curs;
    LOOP
      
      FETCH curs INTO r1;
      EXIT WHEN NOT FOUND;
      
      FETCH NEXT FROM curs INTO r2;
      IF NOT FOUND THEN
          stu_id := r1.sid;
          scnd_score := NULL;
          RETURN NEXT;
          EXIT;
      END IF;
      
      IF r1.sid - r2.sid = 0 THEN
        stu_id := r1.sid;
        scnd_score := r2.score;
        RETURN NEXT;
        
        current_sid = r1.sid;
        
        WHILE r1.sid = current_sid LOOP
          FETCH NEXT FROM curs INTO r1; 
        END LOOP;
        
      ELSE
        stu_id := r1.sid;
        scnd_score := NULL;
        RETURN NEXT;
        
      END IF;
      
      MOVE RELATIVE -1 FROM curs;
      
    END LOOP;
    
    CLOSE curs;
END;

$$ LANGUAGE plpgsql;







CREATE OR REPLACE FUNCTION slist_scnd_highest() 
RETURNS TABLE ( stu_id integer, second_highest_score integer ) AS $$ 
DECLARE 
  max_score integer; 
  num_records_for_current_stud integer;
  curs CURSOR FOR (SELECT sid, score from exams order by sid, score desc); 
  r1 RECORD;
  r2 RECORD;

BEGIN 
  OPEN curs;
  
  LOOP
  
  FETCH curs into r1;
  EXIT WHEN NOT FOUND;
  
  FETCH RELATIVE 1 FROM curs INTO r2;
  
  IF r1.sid <> r2.sid THEN
    stu_id := r1.sid;
    second_highest_score := NULL;
    RETURN NEXT;
    MOVE RELATIVE -1 FROM CURS;
  ELSE
    stu_id := r2.sid;
    second_highest_score := r2.score;
    RETURN NEXT;
    SELECT count(score) INTO num_records_for_current_stud
    from exams
    where sid = r2.sid;
    IF num_records_for_current_stud-2 <> 0 THEN
    MOVE RELATIVE num_records_for_current_stud-2 FROM curs;
    END IF;
  END IF;
  
  END LOOP;
  
  CLOSE curs;
  
END; 
$$ LANGUAGE plpgsql; 


select list_scnd_highest();

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About PostgreSQL

PostgreSQL is a open source relational database system and is also knows as Postgres.

Key Features:

  • Postgres is not only free and open-source but also it is highly extensible.
  • Custom Data types and funtions from various programming languaues can be introduced and the good part is compiling entire database is not required.
  • ACID(Atomicity, Consistency, Isolation, Durability) compliant.
  • First DBMS which implemented Multi-version concurrency control (MVCC) feature.
  • It's the default database server for MacOS.
  • It supports all major operating systems like Linux, Windows, OpenBSD,FreeBSD etc.

Syntax help

1. CREATE

CREATE command is used to create a table, schema or an index.

Syntax:

         CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

2. ALTER

ALTER command is used to add, modify or delete columns or constraints from the database table.

Syntax

ALTER TABLE Table_name ADD column_name datatype;

3. TRUNCATE:

TRUNCATE command is used to delete the data present in the table but this will not delete the table.

Syntax

TRUNCATE table table_name;

4. DROP

DROP command is used to delete the table along with its data.

Syntax

DROP TABLE table_name;

5. RENAME

RENAME command is used to rename the table name.

Syntax

ALTER TABLE table_name1 RENAME to new_table_name1;

6. INSERT

INSERT Statement is used to insert new records into the database table.

Syntax

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

7. SELECT

Select statement is used to select data from database tables.

Syntax:

SELECT column1, column2, ...
FROM table_name;

8. UPDATE

UPDATE statement is used to modify the existing values of records present in the database table.

Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

9. DELETE

DELETE statement is used to delete the existing records present in the database table.

Syntax

DELETE FROM table_name where condition;