Concat all column values in sql

Question

How to concat all column values from differenct rows returned from a sql query into one value? This is an example:

a query returns:

FOO
------
RES1

RES2
         


        

Answer 1

Here is the answer you are looking for; I had a feeling the solution lay in the CONNECT BY operation, I just hadn't used the SYS_CONNECT_BY_PATH pseudocolumn before (which displays the full path to the node in a tree, separating node names by a "/"). Assuming that your set of "foo" values before are multiple rows in a table, grouped by a column "myKey", e.g.:

myKey    foo
-------- ----------
group 1  apple
group 1  orange
group 1  pear
group 2  ape
group 2  bear
group 2  kitten

you can treat the data as if it were a tree schema, and pretend that the values of each group represent nodes going down a branch. In that case, you'd do this:

  SELECT myKey
       , SUBSTR(MAX(REPLACE(SYS_CONNECT_BY_PATH(foo, '/')
                           ,'/'
                           ,' '
                           )
                   )
               ,2
               ) FooConcat
    FROM ( SELECT MyKey
                , Foo
                , row_number() OVER (Partition by myKey order by myKey) NodeDepth
             FROM MyTable
         )
   START WITH NodeDepth = 1
 CONNECT BY PRIOR myKey = myKey
     AND PRIOR NodeDepth = NodeDepth -1
GROUP BY myKey
;

Of course, the order of the concatenated values would be random; if your table had another column ("bar") that you could use as an ordering field that was ascending and contiguous, you could dispense with the subquery (which only exists to put an imaginary depth to the tree) and use the table directly, replacing NodeDepth with bar.