How do I print a triangle of stars using PL/SQL - plsql

Question

Is it practically possible to create a triangle of stars like this as below in PL/SQL. I know that this could be done easily in any other programming language like C,C++,Java but want to know whether it is really possible with just SQL or PL/SQL. This is for my homework and I should use conditional clauses (IF THEN ELSE), loops(FOR, WHILE).
*
***
*****
*******
*********
***********
*************
and
*****
***
*

Answer 1

Try this.
The first loop will print the stars in triangle and the second loop will reverse it.
In PL/SQL:
BEGIN
FOR i IN 1 .. :p
LOOP
DBMS_OUTPUT.put_line (LPAD (LPAD ('*', i, '*'), :p + 1, ' '));
END LOOP;
FOR i IN 1 .. :p
LOOP
DBMS_OUTPUT.put_line (LPAD (LPAD ('*', :p-i, '*'), :p + 1, ' '));
END LOOP;
END;
In SQL:
SELECT LPAD (LPAD ('*', level, '*'), :p + 1, ' ') a
FROM DUAL
CONNECT BY LEVEL <= :p;

Answer 2

This can be done purely in sql (in Oracle), like so:
SELECT RPAD(' ', :p_num_triangle_rows - LEVEL) || RPAD('*', LEVEL * 2 -1, '*') || RPAD(' ', :p_num_triangle_rows - LEVEL) triangle
FROM dual
CONNECT BY LEVEL <= :p_num_triangle_rows
ORDER BY CASE WHEN :p_ascending_or_descending = 'a' THEN LEVEL END ASC,
CASE WHEN :p_ascending_or_descending = 'd' THEN LEVEL END DESC;
p_num_triangle_rows := 20, p_ascending_or_desc := 'a':
TRIANGLE
--------------------------------------------------------------------------------
*
***
*****
*******
*********
***********
*************
***************
*****************
*******************
*********************
***********************
*************************
***************************
*****************************
*******************************
*********************************
***********************************
*************************************
***************************************
p_num_triangle_rows := 3, p_ascending_or_desc := 'd':
TRIANGLE
--------------------------------------------------------------------------------
*****
***
*
ETA: Here is a PL/SQL version that will do what you're after:
DECLARE
PROCEDURE produce_triangle_rows (p_num_triangle_rows IN NUMBER,
p_ascending_or_descending IN VARCHAR2 DEFAULT 'a')
IS
BEGIN
dbms_output.put_line('p_num_triangle_rows = '|| p_num_triangle_rows ||', p_ascending_or_descending = ' || p_ascending_or_descending);
FOR i IN 1..p_num_triangle_rows
LOOP
CASE WHEN p_ascending_or_descending = 'a' THEN
dbms_output.put_line(RPAD(' ', p_num_triangle_rows - i) || RPAD('*', i * 2 - 1, '*') || RPAD(' ', p_num_triangle_rows - i));
WHEN p_ascending_or_descending = 'd' THEN
dbms_output.put_line(RPAD(' ', i - 1) || RPAD('*', 2 * (p_num_triangle_rows - i) + 1, '*') || RPAD(' ', i - 1));
END CASE;
END LOOP;
END produce_triangle_rows;
BEGIN
produce_triangle_rows(p_num_triangle_rows => 5,
p_ascending_or_descending => 'a');
produce_triangle_rows(p_num_triangle_rows => 3,
p_ascending_or_descending => 'd');
END;
/
p_num_triangle_rows = 5, p_ascending_or_descending = a
*
***
*****
*******
*********
p_num_triangle_rows = 3, p_ascending_or_descending = d
*****
***
*
Note that I've wrapped the procedure in an anonymous block purely so I could call it with different parameters. You would just create the produce_triangle_rows procedure on its own and then call it appropriately.

Answer 3

Try this
declare #count int,#num int,#num1 int, #space int, #str varchar(50)
set #count = 3 set #num = 1
while(#num<=#count)
begin
set #num1 = 0 set #space = #count-#num
while (#num1<#num)
begin
if #str is null
set #str = '* '
else
set #str = #str+'* ' set #num1 = #num1+1
end
print (space(#space)+#str)
set #num = #num+1 set #str = null
end
Or
Declare #x varchar(20)=0,#y varchar(20)=5
while(#y>0)
begin
print space(#y)+replicate('*',#x)+replicate('*',#x+1)
set #y=#y-1
set #x=#x+1
end

Answer 4

I found the problem fun, so I solved it in PostgreSQL. Unfortunately repeating characters seems not really be a standardized feature. Here are the syntax to use for the most common RDBMSes:
PostgreSQL : repeat('*', n)
Oracle : rpad('', n, '*')
MS SQL Server : replicate('*', n)
MySQL : repeat('*', n)
First create some table with numbers up to whatever is the biggest triangle you can imagine:
create table n10 (n) as
select 0 union
select 1 union
select 2 union
select 3 union
select 4 union
select 5 union
select 6 union
select 7 union
select 8 union
select 9;
create table n1000 (n) as
select 100 * a1.n + 10 * a2.n + a3.n
from n10 a1 cross join n10 a2 cross join n10 a3;
Then to make a triangle of size 5 (replace 5 by any number between 0 and 1000 you want):
with s (s) as (select 5)
select
repeat(' ', s - n - 1) ||
repeat('*', 2 * n + 1) ||
repeat(' ', s - n - 1)
from n1000 cross join s
where n < s
order by n;
with s (s) as (select 5)
select
repeat(' ', s - n - 1) ||
repeat('*', 2 * n + 1) ||
repeat(' ', s - n - 1)
from n1000 cross join s
where n < s
order by n desc;