SQL:Transponering af rækker til kolonner

Jeg kan ikke tale om MySQL, men i PostgreSQL kan du bruge krydstabulatorfunktion fra tablefunc modul:

CREATE OR REPLACE VIEW PersonAttributePivot AS
    SELECT PersonId AS ID, Age, HairColor
    FROM crosstab
    (
       'SELECT PersonId, Key, Value FROM PersonAttribute',
       'SELECT DISTINCT Key FROM PersonAttribute ORDER BY Key'
    )
    AS
    (
        PersonId integer,
        Age text,
        HairColor text
    );

Deltag i forespørgsel:

SELECT id, name, age, haircolor
FROM Person JOIN PersonAttributePivot USING(id)
ORDER BY id;

Ønsket resultat:

 id |    name    | age | haircolor 
----+------------+-----+-----------
  1 | Joe Bloggs | 27  | 
  2 | Jane Doe   |     | Brown
(2 rows)

Som du ser, har jeg lagt en eksplicit liste over kolonner i PersonAttributePivot udsigt. Jeg kender ikke nogen "automatisk-pivot"-oprettelsesmåde med implicit kolonneliste.

EDIT:

For store kolonneliste (under forudsætning af altid text type) som en løsning ser jeg sådan lidt ændret tilgang:

Dynamisk typeoprettelse (her trivielt Java-baseret):

Class.forName("org.postgresql.Driver");
Connection c =
        DriverManager.getConnection("jdbc:postgresql://localhost/postgres", "postgres", "12345");
Statement s = c.createStatement();
ResultSet rs = s.executeQuery("SELECT DISTINCT Key FROM PersonAttribute ORDER BY Key");
List<String> columns = new ArrayList<String>();

while (rs.next())
    columns.add(rs.getString(1));

System.out.println("CREATE TYPE PersonAttributePivotType AS (");
System.out.println("\tPersonId integer,");
for (int i = 0; i < columns.size(); ++i)
{
    System.out.print("\t" + columns.get(i) + " text");
    if (i != columns.size() - 1)
        System.out.print(",");
    System.out.println();
}
System.out.println(");");

Resultat:

CREATE TYPE PersonAttributePivotType AS (
    PersonId integer,
    Age text,
    HairColor text
);

Funktionsindpakning:

CREATE OR REPLACE FUNCTION crosstabPersonAttribute(text, text)
    RETURNS setof PersonAttributePivotType
    AS '$libdir/tablefunc','crosstab_hash' LANGUAGE C STABLE STRICT;

Automatisk visningsoprettelse:

CREATE OR REPLACE VIEW PersonAttributePivot AS
    SELECT * FROM crosstabPersonAttribute
    (
       'SELECT PersonId, Key, Value FROM PersonAttribute',
       'SELECT DISTINCT Key FROM PersonAttribute ORDER BY Key'
    );

Resultat:

TABLE PersonAttributePivot;
 personid | age | haircolor
----------+-----+-----------
        1 | 27  |
        2 |     | Brown
(2 rows)