Select where record does not exists - sql

Question

I am trying out my hands on oracle 11g. I have a requirement such that I want to fetch those id from list which does not exists in table.
For example:
SELECT * FROM STOCK
where item_id in ('1','2'); // Return those records where result is null
I mean if item_id '1' is not present in db then the query should return me 1.
How can I achieve this?

Answer 1

You need to store the values in some sort of "table". Then you can use left join or not exists or something similar:
with ids as (
select 1 as id from dual union all
select 2 from dual
)
select ids.id
from ids
where not exists (select 1 from stock s where s.item_id = ids.id);

Answer 2

You can use a LEFT JOIN to an in-line table that contains the values to be searched:
SELECT t1.val
FROM (
SELECT '1' val UNION ALL SELECT '2'
) t1
LEFT JOIN STOCK t2 ON t1.val = t2.item_id
WHERE t2.item_id IS NULL

Answer 3

First create the list of possible IDs (e.g. 0 to 99 in below query). You can use a recursive cte for this. Then select these IDs and remove the IDs already present in the table from the result:
with possible_ids(id) as
(
select 0 as id from dual
union all
select id + 1 as id from possible_ids where id < 99
)
select id from possible_ids
minus
select item_id from stock;

Answer 4

A primary concern of the OP seems to be a terse notation of the query, notably the set of values to test for. The straightforwwrd recommendation would be to retrieve these values by another query or to generate them as a union of queries from the dual table (see the other answers for this).
The following alternative solution allows for a verbatim specification of the test values under the following conditions:
There is a character that does not occur in any of the test values provided ( in the example that will be - )
The number of values to test stays well below 2000 (to be precise, the list of values plus separators must be written as a varchar2 literal, which imposes the length limit ). However, this should not be an actual concern - If the test involves lists of hundreds of ids, these lists should definitely be retrieved froma table/view.
Caveat
Whether this method is worth the hassle ( not to mention potential performance impacts ) is questionable, imho.
Solution
The test values will be provided as a single varchar2 literal with - separating the values which is as terse as the specification as a list argument to the IN operator. The string starts and ends with -.
'-1-2-3-156-489-4654648-'
The number of items is computed as follows:
select cond, regexp_count ( cond, '[-]' ) - 1 cnt_items from (select '-1-2-3-156-489-4654648-' cond from dual)
A list of integers up to the number of items starting with 1 can be generated using the LEVEL pseudocolumn from hierarchical queries:
select level from dual connect by level < 42;
The n-th integer from that list will serve to extract the n-th value from the string (exemplified for the 4th value) :
select substr ( cond, instr(cond,'-', 1, 4 )+1, instr(cond,'-', 1, 4+1 ) - instr(cond,'-', 1, 4 ) - 1 ) si from (select cond, regexp_count ( cond, '[-]' ) - 1 cnt_items from (select '-1-2-3-156-489-4654648-' cond from dual) );
The non-existent stock ids are generated by subtracting the set of stock ids from the set of values. Putting it all together:
select substr ( cond, instr(cond,'-',1,level )+1, instr(cond,'-',1,level+1 ) - instr(cond,'-',1,level ) - 1 ) si
from (
select cond
, regexp_count ( cond, '[-]' ) - 1 cnt_items
from (
select '-1-2-3-156-489-4654648-' cond from dual
)
)
connect by level <= cnt_items + 1
minus
select item_id from stock
;