如何从分组行中提取值到 Oracle SQL 中的特定列？

Question

Suppose I have a table like this in Oracle:

+----------+-----------+--------+
| PersonId | ValueType | Value  |
+----------+-----------+--------+
|        1 | FirstName | John   |
|        1 | LastName  | Smith  |
|        2 | FirstName | John   |
|        2 | LastName  | Doe    |
|        2 | City      | London |
+----------+-----------+--------+

How can I select the data like the following:

+----------+-----------+----------+--------+
| PersonId | FirstName | LastName |  City  |
+----------+-----------+----------+--------+
|        1 | John      | Smith    |        |
|        2 | John      | Doe      | London |
+----------+-----------+----------+--------+

?

Answer 1

Try with case expressions to pivot your data.

select
    PersonId,
    max(case when ValueType = 'FirstName' then Value end) as FirstName,
    max(case when ValueType = 'LastName' then Value end) as LastName,
    max(case when valueType = 'City' then value end) City
from yourTable
group by
    PersonId

Answer 2

You can pivot your dataset with conditional aggregation:

select
    personid,
    max(case when valuetype = 'FirstName' then value end) firstname,
    max(case when valuetype = 'LastName'  then value end) lastname,
    max(case when valuetype = 'City'      then value end) city
from mytable
group by personid

Answer 3

The old way of pivoting (and, importantly, the SQL Standard compliant way) uses conditional aggregation, as shown in zealous's and GMB's answers.

Oracle introduced the pivot (and related unpivot ) operator in version 11.1, that is, a very long time ago. I illustrate that approach below. These operators are particularly helpful when we need to pivot (or unpivot) multiple columns at a time; however, that's not the case in this thread.

Setting up the test table:

create table person (personid, valuetype, value) as
  select 1, 'FirstName', 'John'   from dual union all 
  select 1, 'LastName' , 'Smith'  from dual union all
  select 2, 'FirstName', 'John'   from dual union all
  select 2, 'LastName' , 'Doe'    from dual union all
  select 2, 'City'     , 'London' from dual
;

Query and output:

select personid, firstname, lastname, city
from   person
pivot  (min(value) for valuetype in ( 'FirstName' as firstname
                                    , 'LastName'  as lastname
                                    , 'City'      as city
                                    )
       )
;

PERSONID FIRSTNAME LASTNAME  CITY  
-------- --------- --------- ------
       1 John      Smith        
       2 John      Doe       London

And - perhaps more as a curiosity (with more serious applicability, maybe, to other, harder problems) - here is a solution using match_recognize , introduced in Oracle 12.1. Importantly, unlike any other solutions, this approach does not use aggregation of any kind.

select personid, firstname, lastname, city
from   person
match_recognize
  (
    partition by personid
    measures  f.value as firstname
           ,  l.value as lastname
           ,  c.value as city
    pattern   ( (f|l|c)* )
    define    f as valuetype = 'FirstName'
         ,    l as valuetype = 'LastName'
         ,    c as valuetype = 'City'
  )
;