SQL Pivot or something else?

Question

I have a pre-existing table (so I can't change this table) like this:

Company     GLSeg1     GLSeg2     GLSeg3
XXX         00003      NULL       00001
YYY         00002      00004      NULL

I would like to create a temp table like this, selecting for just one company:

When querying for XXX the table should look like this:

GLSeg       Value
1           00003
2           NULL
3           00001

When querying for YYY the table should look like this:

GLSeg       Value
1           00002
2           00004
3           NULL

I have looked at the pivot function but am not seeing a way to create the temp table as needed.

Answer 1

using cross apply(values ..) to unpivot your data:

select t.Company, v.GLSeg, v.Value
from t
  cross apply (values 
    (1,glseg1),(2,glseg2),(3,glseg3)
  ) v (GLSeg,Value)

rextester demo: http://rextester.com/ZKTD58113

returns:

+---------+-------+-------+
| Company | GLSeg | Value |
+---------+-------+-------+
| xxx     |     1 | 00003 |
| xxx     |     2 | NULL  |
| xxx     |     3 | 00001 |
| yyy     |     1 | 00002 |
| yyy     |     2 | 00004 |
| yyy     |     3 | NULL  |
+---------+-------+-------+

---

For just one company:

select v.GLSeg, v.Value
from t
  cross apply (values 
    (1,glseg1),(2,glseg2),(3,glseg3)
  ) v (GLSeg,Value)  
where t.company = 'xxx'

returns:

+-------+-------+
| GLSeg | Value |
+-------+-------+
|     1 | 00003 |
|     2 | NULL  |
|     3 | 00001 |
+-------+-------+