What SQL query would produce these results? - sql

Question

Given this data:
Name Property Value
---------- ---------- ----------
Bob Hair Red
Bob Eyes Blue
Fred Hair Brown
Fred Height Tall
what SQL would be required to produce these results?
Property Bob Fred
---------- ---------- ----------
Hair Red Brown
Eyes Blue
Height Tall
I'm using SQL Server 2008, but a generic solution would be nice.

Answer 1

You did not specify what RDBMS you are using but this is a pivot. You can use an aggregate function and a CASE expression in all databases:
select property,
max(case when name='Bob' then value else '' end) Bob,
max(case when name='Fred' then value else '' end) Fred
from yourtable
group by property
See SQL Fiddle with Demo
If you are using a database that has a PIVOT function (SQL Server 2005+/Oracle 11g+), then your code will be similar to this:
select *
from
(
select property, name, value
from yourtable
) src
pivot
(
max(value)
for name in (Bob, Fred)
) piv
See SQL Fiddle with Demo
The above queries work great, if you know the name values ahead of time, but if you don't then you will want to use dynamic sql:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(name)
from yourtable
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT property,' + #cols + ' from
(
select property, name, value
from yourtable
) x
pivot
(
max(value)
for name in (' + #cols + ')
) p '
execute(#query)
See SQL Fiddle with Demo
All three will produce the same result:
| PROPERTY | BOB | FRED |
---------------------------
| Eyes | Blue | |
| Hair | Red | Brown |
| Height | | Tall |

Answer 2

Here's the old-fashioned way, of course assuming that each (Name, Property) is unique:
SELECT Properties.Property, Bob.Value, Fred.Value
FROM
(
SELECT DISTINCT Property
FROM myTable
) Properties
LEFT OUTER JOIN
(
SELECT Property, Value
FROM myTable
WHERE Name = 'Bob'
) Bob ON Properties.Property = Bob.Property
LEFT OUTER JOIN
(
SELECT Property, Value
FROM myTable
WHERE Name = 'Fred'
) Fred ON Properties.Property = Fred.Property
Of course you can only do this if you know the columns ahead of time. You could make and execute dynamic SQL if you did not, but this is not without its issues.
Depending on your RDBMS you may be able to use a pivot query instead, which will simplify the syntax (or make it possible if you have an unknown number/names of people)