Question

Here’s my problem:

I have a table with 4 columns (type = array, one-dimension) with values like:

   ID        c1             c2           c3

   1      {1, 2, 3}    {10, 20, 30}   {100, 200, 300}
   2      {4, 5, 6}    {11, 22, 33}   {111, 222, 333}

I was wondering if it is possible to get a result like the following:

   select ID, c1, c2, c3 from t1 where c3 = 200 (<---- pseudo-statement!)

Result:

   1, 2, 20, 200

or

   select ID, c1, c2, c3 from t1 where c3 = 333 

Result:

    1, 6, 33, 333

So what I want is to get the corresponding values of the value in the where-statement.

Is there a way to get a solution for this?

Answer 1

(Edit1: simplified, Edit2: wider scope)

Solutions for any array-length. Also returns all hits, even at multiple positions in one or more arrays at the same time.

If you know the fixed length of the one-dimensional array, you can hard-code it in generate_series(), for the simplest and fastest solution:

SELECT id, c1[i], c2[i], c3[i]
FROM   tbl, generate_series(1, 3) i
WHERE  c3[i] = 200;

---

If all arrays in c3 have the same unknown length, you can generalize at very little cost:

SELECT id, c1[i], c2[i], c3[i]
FROM   tbl, generate_subscripts((SELECT c3 FROM tbl LIMIT 1), 1) s(i)
WHERE  c3[i] = 200;

Note that I use the convenient function generate_subscripts() here.
For a greater subscripts than the upper limit, array elements are just NULL and drop out of the query.

---

If the unknown length of the array in c3 actually varies, you can generalize some more, at a higher cost:

SELECT id, c1[i], c2[i], c3[i]
FROM   tbl
FROM   tbl, generate_series(1, (SELECT max(array_upper(c3, 1)) FROM tbl)) s(i)
WHERE  c3[i] = 200;

---

Finally, for non-standard array subscripts in addition, the same could be done like this:

SELECT id, c1[i], c2[i], c3[i]
FROM   tbl
     , generate_subscripts((SELECT c3 FROM tbl
                            ORDER  BY array_length(c3,1) DESC LIMIT 1), 1) s(i)
WHERE  c3[i] = 200;

---

Instant testbed:

WITH tbl (id, c1, c2, c3) AS (
    VALUES
     (1, '{1, 2, 3}'::int[], '{10, 20, 30}'::int[], '{100, 200, 300}'::int[])
    ,(2, '{4, 5, 6}', '{11, 22, 33}', '{111, 222, 333}')
-- un-comment to test 333 in all positions of c3 and varying array length
--  ,(3, '{7, 8, 9, 10}', '{14, 25}', '{333, 333, 333, 333}')
    )
SELECT id, c1[i], c2[i], c3[i]
FROM tbl
    ,generate_subscripts((SELECT c3 FROM tbl
                          ORDER  BY array_length(c3,1) DESC LIMIT 1), 1) s(i)
WHERE  c3[i] = 333;