execute SQL query stored in a table - oracle

Question

I have a table having one of the columns that stores SQL query returning ids or it stores comma separated ids.
create table to store query or ids(separated by ,)
create table test1
(
name varchar(20) primary key,
stmt_or_value varchar(500),
type varchar(50)
);
insert into test1 (name, stmt_or_value, type)
values ('first', 'select id from data where id = 1;','SQL_QUERY')
insert into test1 (name, stmt_or_value, type)
values ('second', '1,2,3,4','VALUE')
data table is as follows
create table data
(
id number,
subject varchar(500)
);
insert into data (id, subject) values (1, 'test subject1');
insert into data (id, subject) values (2, 'test subject2');
insert into data (id, subject) values (3, 'test subject2');
I am not able to formulate query that will return values after either executing stored sql or parsing stored ids based on the value of name.
select id, subject
from data
where id in( EXECUTE IMMEDIATE stmt_or_value
where type='SQL_QUERY'
and name = 'first') or
( parse and return ids
from stmt_or_value
where type='VALUE'
and name = 'second')
Could you please help me in this.
Parsing comma separated value is done, I basically need help in below first part of the query:
( EXECUTE IMMEDIATE stmt_or_value
where type='SQL_QUERY'
and name = 'first')

Answer 1

This seems a very peculiar requirement, and one which will be difficult to solve in a robust fashion. STMT_OR_VALUE is the embodiment of the One Column Two Usages anti-pattern. Furthermore, resolving STMT_OR_VALUE requires flow control logic and the use of dynamic SQL. Consequently it cannot be a pure SQL solution: you need to use PL/SQL to assemble and execute the dynamic query.
Here is a proof of concept for a solution. I have opted for a function which you can call from SQL. It depends on one assumption: every query string you insert into TEST1.STMT_OR_VALUE has a projection of a single numeric column and every value string is a CSV of numeric data only. With this proviso it is simple to construct a function which either executes a dynamic query or tokenizes the string into a series of numbers; both of which are bulk collected into a nested table:
create or replace function get_ids (p_name in test1.name%type)
return sys.odcinumberlist
is
l_rec test1%rowtype;
return_value sys.odcinumberlist;
begin
select * into l_rec
from test1
where name = p_name;
if l_rec.type = 'SQL_QUERY' then
-- execute a query
execute immediate l_rec.stmt_or_value
bulk collect into return_value;
else
-- tokenize a string
select xmltab.tkn
bulk collect into return_value
from ( select l_rec.stmt_or_value from dual) t
, xmltable( 'for $text in ora:tokenize($in, ",") return $text'
passing stmt_or_value as "in"
columns tkn number path '.'
) xmltab;
end if;
return return_value;
end;
/
Note there is more than one way of executing a dynamic SQL statement and a multiplicity of ways to tokenize a CSV into a series of numbers. My decisions are arbitrary: feel free to substitute your preferred methods here.
This function can be invoked with a table() call:
select *
from data
where id in ( select * from table(get_ids('first'))) -- execute query
or id in ( select * from table(get_ids('second'))) -- get string of values
/
The big benefit of this approach is it encapsulates the logic around the evaluation of STMT_OR_VALUE and hides use of Dynamic SQL. Consequently it is easy to employ it in any SQL statement whilst retaining readability, or to add further mechanisms for generating a set of IDs.
However, this solution is brittle. It will only work if the values in the test1 table obey the rules. That is, not only must they be convertible to a stream of single numbers but the SQL statements must be valid and executable by EXECUTE IMMEDIATE. For instance, the trailing semi-colon in the question's sample data is invalid and would cause EXECUTE IMMEDIATE to hurl. Dynamic SQL is hard not least because it converts compilation errors into runtime errors.

Answer 2

Following is the set up data used for this example:
create table test1
(
test_id number primary key,
stmt_or_value varchar(500),
test_type varchar(50)
);
insert into test1 (test_id, stmt_or_value, test_type)
values (1, 'select id from data where id = 1','SQL_QUERY');
insert into test1 (test_id, stmt_or_value, test_type)
values (2, '1,2,3,4','VALUE');
insert into test1 (test_id, stmt_or_value, test_type)
values (3, 'select id from data where id = 5','SQL_QUERY');
insert into test1 (test_id, stmt_or_value, test_type)
values (4, '3,4,5,6','VALUE');
select * from test1;
TEST_ID STMT_OR_VALUE TEST_TYPE
1 select id from data where id = 1 SQL_QUERY
2 1,2,3,4 VALUE
3 select id from data where id = 5 SQL_QUERY
4 3,4,5,6 VALUE
create table data
(
id number,
subject varchar(500)
);
insert into data (id, subject) values (1, 'test subject1');
insert into data (id, subject) values (2, 'test subject2');
insert into data (id, subject) values (3, 'test subject3');
insert into data (id, subject) values (4, 'test subject4');
insert into data (id, subject) values (5, 'test subject5');
select * from data;
ID SUBJECT
1 test subject1
2 test subject2
3 test subject3
4 test subject4
5 test subject5
Below is the solution:
declare
sql_stmt clob; --to store the dynamic sql
type o_rec_typ is record(id data.id%type, subject data.subject%type);
type o_tab_typ is table of o_rec_typ;
o_tab o_tab_typ; --to store the output records
begin
--The below SELECT query generates the required dynamic SQL
with stmts as (
select (listagg(stmt_or_value, ' union all ') within group(order by stmt_or_value))||' union all ' s
from test1 t
where test_type = 'SQL_QUERY')
select
q'{select id, subject
from data
where id in (}'||
nullif(s,' union all ')||q'{
select distinct to_number(regexp_substr(s, '[^,]+', 1, l)) id
from (
select level l,
s
from (select listagg(stmt_or_value,',') within group(order by stmt_or_value) s
from test1
where test_type = 'VALUE') inp
connect by level <= length (regexp_replace(s, '[^,]+')) + 1))}' stmt into sql_stmt
from stmts; -- Create the dynamic SQL and store it into the clob variable
--execute the statement, fetch and display the output
execute immediate sql_stmt bulk collect into o_tab;
for i in o_tab.first..o_tab.last
loop
dbms_output.put_line('id: '||o_tab(i).id||' subject: '||o_tab(i).subject);
end loop;
end;
Output:
id: 1 subject: test subject1
id: 2 subject: test subject2
id: 3 subject: test subject3
id: 4 subject: test subject4
id: 5 subject: test subject5
Learnings:
Avoid using key words for table and column names.
Design application tables effectively to serve current and reasonable future requirements.
The above SQL will work. Still it is wise to consider reviewing the table design because, the complexity of the code will keep increasing with changes in requirements in future.
Learned how to convert comma separated values into records. "https://asktom.oracle.com/pls/apex/f?p=100:11:::NO::P11_QUESTION_ID:9538583800346706523"

Answer 3

declare
my_sql varchar2(1000);
v_num number;
v_num1 number;
begin
select stmt_or_value into my_sql from test1 where ttype='SQL_QUERY';
execute immediate my_sql into v_num;
select id into v_num1 from data where id=v_num;
dbms_output.put_line(v_num1);
end;
Answer for part 1.Please check.