Postgres SQL function string_to_array - arrays

Question

I have a table:
c1|c2|c3|c4
-----+--+--+----
a b c 10
a a b 20
c a c 10
b b c 10
c b c 30
I want to write a function where the inputs are 3 strings / text eg ('a b c, b d, c'), compare every element to each other, find if a row exist with this combination, an sum the number of the 4th (c4) column up. But if there is a constellation of b a c or c a b it would match a b c 10. If there is a row like b c c then it wont be a row like c b b. Every matchup is unique.
I think the best would be to use string_to_array(text, text).
I put together some pseudo code, but no idea how to write it in SQL. Maybe the logic is wrong too.
function (x,y,z)
res = 0
x_array = string_to_array(x, ' ')
y_array = string_to_array(y, ' ')
z_array = string_to_array(z, ' ')
foreach(x_item in x_array)
foreach(y_item in y_array)
foreach(z_item in z_array)
if (c1 = (x_item || y_item || z_item ) && c2 = (x_item || y_item || z_item ) && c3 = (x_item || y_item || z_item ))
res++
EDIT
First off all there was a mistake in the example table. There was a row a b c and c b a. It cant be. a b c = c b a ! and each row must be unique.
example: three text inputs a b c | b c | c
each element vs each element: a b c , a c c, b b c, b c c, c b c, c c c
a b c = 10;
a c c (is the same as c a c) = 10;
b b c = 10;
b c c (is the same as c b c) = 30;
c b c = 30;
c c c (no match) = 0; result = 90

Answer 1

I think this might be what you want:
Return the sum of column c4 from all rows where a given set of three tokens matches the columns (c1, c2, c3).
Simple version
Much simpler with contains #> and is contained <# by operators:
SELECT sum(c4) AS sum_of_matching_c4
FROM tbl
WHERE ARRAY[c1,c2,c3] <# ARRAY['b', 'a', 'c'] -- strings in arbitrary order
AND ARRAY[c1,c2,c3] #> ARRAY['b', 'a', 'c'];
Sorry, that would fail for ('b', 'c', 'c') vs. ('c', 'b', 'b').
Slow and sure
WITH i(arr) AS (
SELECT ARRAY(VALUES ('b'), ('c'), ('c') ORDER BY 1) -- input once
) -- in arbitrary order
SELECT sum(c4) AS sum_of_matching_c4
FROM (
SELECT c4, array_agg(x ORDER BY x) AS arr
FROM (
SELECT ctid, c4, unnest(ARRAY[c1,c2,c3]) AS x
FROM tbl t, i
WHERE ARRAY[c1,c2,c3] <# arr -- optional pre-selection
AND ARRAY[c1,c2,c3] #> arr -- for better performance?
) a
GROUP BY ctid, c4
) b
JOIN i USING (arr)
-> sqlfiddle demo.
The major difficulty is to order the values of the columns within the row.
For your input (3 strings) I achieve this in the WHERE clause with a VALUE expression in the CTE which I order right away and collect it in an array. I use a CTE for convenience, so we have to enter values in one place only.
It's more complicated for the row values. I put the three columns in an array and break that up to rows with unnest(). As you did not provide a primary key, I use the ctid as ad-hoc surrogate primary key instead - which I need for the GROUP BY to stuff the now sorted (c1, c2, c3) into an array.
Finally I sum up all c4 of rows where the now sorted arrays match exactly.
Note: I expressly do not use string_agg() because that does not produce distinct results. Consider:
'abc' 'cde' 'fgh'
'ab' 'ccdef' 'gh'
.. resulting int the same string if concatenated.
Index / Performance
You might consider to save pre-ordered data to speed up queries. Doing it on the fly is expensive. I.e. you could pre-generate the sorted array and save it as redundant column which you can then support with an index. Should be faster by several orders of magnitude for the cost of redundant data storage.
If you are dealing with long strings, a solution similar to what I outlined in this related answer on dba.SE might be the best course of action.
Alternatively (preferred!) guarantee that (c1, c2, c3) are always stored in ascending order. You could use a trigger BEFORE INSERT OR UPDATE to keep values within the row ordered. No redundant storage and you can simply create a multi-column index on the three columns and compare to them one by one (instead of comparing the array like in my example).

Answer 2

You don't need to write a function for that.
First, there's no "strings" with postgresql ( sql ) , it's "text" or "varchar".
Second, what you need is an SQL query like this:
SELECT ( DISTINCT ( c1 || c2 || c3 )) AS txtcol, SUM (c4) AS rowsum;
or
SELECT ( DISTINCT ( c1 || c2 || c3 )) AS txtcol, SUM(c4) AS numsum GROUP BY txtcol;
Can't recall the exact syntax at the moment, you need to work it out,
anyway the point is you need to concatenate varchar columns with some built-in
function like CONCAT or "||" operator, and then sum/group by numeric column. All you need
is to concatenate columns, and give resulting all-together column a name.
To be exact, you don't even need to show concatenated column on resulting table,
you could output just sums, and number of rows sumarized for example.
Theoretically you could write SQL function or PL/SQL function for that, but I'm sure it's just not necessary, your case seems to me simple enough to be able to achieve result you want without a function. Built-in sumarizing function SUM() is called "aggregate" function, other examples of aggregating functions are e.g. MIN() or MAX().
Note what you're actually trying to do, is grouping rows by some resulting VARCHAR column by the effect of concatenation per-row.
EDIT: "Arrays" in SQL or procedural SQL is some internally-handled arrays, do not confuse them with relations ( tables in database, nor with tables as SELECT results ). I think you also don't need SQL arrays for that, the task really isn't so hard as it looks like.