I've got a view for reports, that looks something like this:
SELECT
a.id,
a.value1,
a.value2,
b.value1,
/* (+50 more such columns)*/
FROM a
JOIN b ON (b.id = a.b_id)
JOIN c ON (c.id = b.c_id)
LEFT JOIN d ON (d.id = b.d_id)
LEFT JOIN e ON (e.id = d.e_id)
/* (+10 more inner/left joins) */
It joins quite a few tables and returns lots of columns, but indexes are in place and performance is fine.
Now I want to add another column to the result, showing
comma-separated values
ordered by value
from table y
outer joined via intersection table x
if a.value3 IS NULL, else take a.value3
To comma-separate the grouped values I use Tom Kyte's stragg, could use COLLECT later.
Pseudo-code for the SELECT would look like that:
SELECT xx.id, COALESCE( a.value3, stragg( xx.val ) ) value3
FROM (
SELECT x.id, y.val
FROM x
WHERE x.a_id = a.id
JOIN y ON ( y.id = x.y_id )
ORDER BY y.val ASC
) xx
GROUP BY xx.id
What is the best way to do it? Any tips?
