Oracle SQL — Grabbing values from multiple rows

问题:

I have a table like this:

TABLE: FACTS
ID       KEY         VALUE
1        name        Jeremy
1        height      5'11
1        awesomeness 10
2        name        Mark
2        awesomeness 4
3        height      4'6

So, the (ID,KEY) tuple can be considered as a primary key.

I am trying to return rows like this:

ID     NAME     HEIGHT    AWESOMENESS
1      Jeremy   5'11      10
2      Mark     (null)    4
3      (null)   4'6       (null)

So other than by doing a sub-select for each column, how can grab the key values, if they are there, and collect them into my single row? What I tried so far was:

SELECT 
  id,
  CASE WHEN facts.key = 'name' THEN value END name,
  CASE WHEN facts.key = 'height' THEN value END height,
  CASE when facts.key = 'awesomeness' THEN value END awesomeness
FROM
  facts
WHERE
  facts.id in (1,2,3)

But for obvious reasons this returns one row per key that matches, not one row per id.

How can I go about getting this the way I want?

Thanks!

回答1:

You can pivot the data like this in any version of Oracle.

SELECT id,
       MAX( CASE WHEN key = 'name' THEN value ELSE null END ) name,
       MAX( CASE WHEN key = 'height' THEN value ELSE null END ) height,
       MAX( CASE WHEN key = 'awesomeness' THEN value ELSE null END ) awesomeness
  FROM facts
 WHERE id IN (1,2,3)
 GROUP BY id

If you're using 11g, you could also use the PVOT operator.

If this is representative of your data model, though, that sort of entity-attribute data model is generally going to be rather inefficient. You would generally be much better served with a table that had columns for name, height, awesomeness, etc.