Turn SQL statement in a function - sql

Question

How to replace a concrete value with a variable in Oracle SQL? I have
select 5, min(id) from my_table where id > 5 --AND ..
UNION ALL
select 6, min(id) from my_table where id > 6 --AND ..
UNION ALL
....
| 5 | 6 |
| 6 | 8 |
...
How to wrap it in a function executing pseudocode below?
for ( $i in ( select id from my_table)){
UNION ALL
select $i, min(id) from my_table where id > $i
}
Edit: To make it clear, I am looking for a general method to turn a select with hard wired values into a function that accepts variables. Note the --AND part.
Edit2:
Let me translate it in Java.
Qu estion: I have code
System.out.println(1+2+" = 1+2"+ " ");
that returns a sum of two numbers. How to replace concrete 1+2 with any a and b?
Answer:
You need to define
int getSum(int a, int b){ return a+b;}
Now you can write
for(int a : setA){
for(int b : setB){
System.out.println(" " +a+"+"+b+" = "+ getSum(a,b)+" ");
}}
This way you can iterate over all elements of setA and all elements of setB instead of providing concrete values 1 and 2.
I have exactly the same question for SQL. If I have a query that returns a result for a concrete value (Java example: 1,2; SQL example: where id > 6 ) - how to modify it so that SQL iterates over all possible values (obtained by select id from t group by id)?

Answer 1

It looks like you want to get the next ID for each id. That can be done simply by using the lead function:
select
t.id,
lead(t.id) over (order by t.id) as next_id
from
my_table t
If you do want to return it from a function, you would probably need a table function returning a custom table type, because the rowtype to return doesn't match your table structure, so you can't use my_table%rowtype.
The snippet below would create such a row type and matching table type, and a function that would return the same as above query. The last lines contain the same query, now using the function instead of the table:
-- Define a row type (an object).
create or replace type my_row_type as object (
id int,
next_id int
);
-- Define a table type of that row type
create type my_table_type as table of my_row_type;
-- Create a function that returns a table.
create or replace function my_function
return my_table_type
is
result my_table_type;
begin
select
-- Use the rowtype constructor to put the id and next_id into a row object
my_row_type(
t.id,
lead(t.id) over (order by t.id))
-- use bulk collect into to query all rows into the table variable 'result'
bulk collect into
result
from
my_table t;
-- Don't forget to actually return it.
return result;
end;
/
-- Query it by 'casting' the function result to a table.
select
id,
next_id
from
table(my_function);
For more info on table functions, I think this tutorial/article is a good start:
http://stevenfeuersteinonplsql.blogspot.com/2015/04/table-functions-introduction-and.html