Informix - update SET column with results from a subselect - sql

Question

I have a table with a collection column. I want to do a subselect which returns several integers and put the result in that collection column, however I can't find a syntax to do it through SQL. I did it by writing an SQL procedure which does the same thing (put results of SELECT in SET variable and return variable), however I'm trying to do the same without functions. Can it be done?
First, I create a temporary table:
CREATE TEMP TABLE table1 (
id INTEGER
, col2 SET(INT NOT NULL)
)
Then I fill it with test data:
INSERT INTO table1 (id) VALUES (1);
INSERT INTO table1 (id) VALUES (2);
And now this works:
UPDATE table1 SET col2 = SET{1,2};
...but I'm trying to do this and it doesn't work:
UPDATE table1 SET col2 = (SELECT id FROM table1) WHERE id = 1;
It returns this error:
[Error Code: -9632, SQL State: IX000] Value does not match the type of column (col2).

Answer 1

Manipulating SET types in pure SQL is a pain.
Your UPDATE is trying to assign an INTEGER to a SET OF INTEGER, and the error says "you can't do that".
You should be able to do:
UPDATE table1
SET col2 = SET { (SELECT id FROM table1 WHERE id = 1) }
WHERE id = 1;
However, I'm not sure what the correct modification is to get more than one value into the set; the inner WHERE is not there idly.

Answer 2

You can achieve this by using MULTISET and ITEM keyword
the following example will work:
CREATE TEMP TABLE table1 (
id INTEGER
,col2 MULTISET(INT NOT NULL)
);
INSERT INTO table1 (id) VALUES (1);
INSERT INTO table1 (id) VALUES (2);
UPDATE table1 SET col2 = MULTISET{1,2};
UPDATE table1
SET col2 = MULTISET(SELECT ITEM id FROM table1)
WHERE id = 1;
Be aware of the differences between SET and MULTISET
select set{1,2,1,3,1} from systables where tabid=1;
returns SET{1,2,3}
select multiset{1,2,1,3,1} from systables where tabid=1;
returns MULTISET{1,2,1,3,1}