如何在SQL中转置查询结果？

Question

As the result of many subqueries, I have the following table:

+---------------------------------------------+
| register | simulation | hasLimit | approved |
+---------------------------------------------+
|     X    |     Y      |    Z     |    W     |
+---------------------------------------------+

But I want it to be like this:

+----------------+
| register   | X | 
+----------------+
| simulation | Y | 
+----------------+
| hasLimit   | Z | 
+----------------+
| approved   | W | 
+----------------+

In RI would simply transpose using the function t(), however in SQL it seems a bit harder. I've tried to understand the function pivot to apply in this case, but it seems a little strange, since I'm actually just transposing, not pivoting anything.

Answer 1

You seem to want an "unpivot" operation.

Assuming the types of the columns are all compatible, you can use union all :

select 'register' as which, register as value union all
select 'simulation',  simulation union all
select 'hasLimit', hasLimit union all
select 'approved', approved;

Some databases require a FROM clause for each subquery, such as from dual .

This is a very small amount of data. For larger data, I prefer a lateral join, but the syntax (and availability of which) depends on the database.

Answer 2

Given the return from

         SELECT 'x' AS register
              , 'y' AS simulation
              , 'z' AS hasLimit
              , 'w' AS approved

We can wrap that in a set of parens and reference it as an inline view in an outer query.

For example:

SELECT CASE i.n
         WHEN 1 THEN 'register'
         WHEN 2 THEN 'simulation'
         WHEN 3 THEN 'hasLimit'
         WHEN 4 THEN 'approved'
       END AS col1
     , CASE i.n
         WHEN 1 THEN q.register
         WHEN 2 THEN q.simulation
         WHEN 3 THEN q.hasLimit
         WHEN 4 THEN q.approved
       END AS col2
  FROM (
         SELECT 'x' AS register
              , 'y' AS simulation
              , 'z' AS hasLimit
              , 'w' AS approved
       ) q
 CROSS
  JOIN ( SELECT 1 AS n
         UNION ALL SELECT 2
         UNION ALL SELECT 3
         UNION ALL SELECT 4
       ) i
 ORDER
    BY i.n

---

That seems a bit of a rigmarole, given that you already have subqueries that are returning scalar values, we could combine those with UNION ALL set operators

SELECT 'register'  AS col1, ( scalar_subquery_for_x ) AS col2
UNION ALL 
SELECT 'simulation'       , ( scalar_subquery_for_y )
UNION ALL 
SELECT 'hasLimit'         , ( scalar_subquery_for_z )
UNION ALL 
SELECT 'approved'         , ( scalar_subquery_for_w )

IF we need a guaranteed order, we can wrap that whole thing in parens and add an ORDER BY clause. (Without the ORDER BY, we do observe rows are returned "in order" from the UNION ALL , but this behavior is not guaranteed.)

Answer 3

Use a simple UNPIVOT as below,

SELECT Col, Val
FROM <Your Table>
UNPIVOT (Val FOR Col IN([register],[simulation],[hasLimit],[approved])) unpiv