Question

I’m new to SQL and I’m wondering how to pivot a table like:

Col1 Col2 Col3
1     a    w
2     a    x 
1     b    y
2     b    z 

Into

Col1 a b
1    w y
2    x z

I was playing with GROUP BY but I can’t seem to be able to turn unique rows into columns

Answer 1

This can be done using an aggregate function with a CASE expression:

select col1,
  max(case when col2 = 'a' then col3 end) a,
  max(case when col2 = 'b' then col3 end) b
from yourtable
group by col1

See SQL Fiddle with Demo

If you are using an RDBMS with a PIVOT function (SQL Server 2005+ / Oracle 11g+), then your query would be similar to this (Note: Oracle syntax below):

select *
from
(
  select col1, col2, col3
  from yourtable
)
pivot
(
  max(col3)
  for col2 in ('a', 'b')
) 

See SQL Fiddle with Demo

The last way that you can do this is by using multiple joins on the same table:

select t1.col1, 
  t1.col3 a, 
  t2.col3 b
from yourtable t1
left join yourtable t2
  on t1.col1 = t2.col1
  and t2.col2 = 'b'
where t1.col2 = 'a'

See SQL Fiddle with Demo

All give the result:

| COL1 | 'A' | 'B' |
--------------------
|    1 |   w |   y |
|    2 |   x |   z |