Query using a statement within a VARCHAR2 column - database

Question

Is there a way for a select statement to include in the WHERE clause a statement that is contained within the table? For example, the following table:
CREATE TABLE test_tab(
date_column DATE,
frequency NUMBER,
test_statement VARCHAR2(255)
)
/
If
MOD(SYSDATE - DATE, frequency) = 0
were contained within the column test_statement, is there a way to select rows where this is true? The test_statement will vary and not be the same throughout the table. I am able to do this in PL/SQL but looking to do this without the use of PL/SQL.

Answer 1

This kind of dynamic SQL in SQL can created with DBMS_XMLGEN.getXML. Although the query looks a bit odd so you might want to consider a different design.
First, I created a sample table and row using your DDL. I'm not sure exactly what you're trying to do with the conditions, so I simplified them into two rows with simpler conditions. The first row matches the first condition, and neither row matches the second condition.
--Create sample table and row that matches the condition.
CREATE TABLE test_tab(
date_column DATE,
frequency NUMBER,
test_statement VARCHAR2(255)
)
/
insert into test_tab values(sysdate, 1, 'frequency = 1');
insert into test_tab values(sysdate, 2, '1=2');
commit;
Here's the large query, and it only returns the first row, which only matches the first condition.
--Find rows where ROWID is in a list of ROWIDs that match the condition.
select *
from test_tab
where rowid in
(
--Convert XMLType to relational data.
select the_rowid
from
(
--Convert CLOB to XMLType.
select xmltype(xml_results) xml_results
from
(
--Create a single XML file with the ROWIDs that match the condition.
select dbms_xmlgen.getxml('
select rowid
from test_tab where '||test_statement) xml_results
from test_tab
)
where xml_results is not null
)
cross join
xmltable
(
'/ROWSET/ROW'
passing xml_results
columns
the_rowid varchar2(128) path 'ROWID'
)
);

Answer 2

This calls for dynamic SQL, so - yes, it is PL/SQL that handles it. I don't think that SQL layer is capable of doing it.
I don't know what you tried so far, so - just an idea: a function that returns ref cursor might help, e.g.
SQL> create table test (date_column date, frequency number, test_statement varchar2(255));
Table created.
SQL> insert into test values (trunc(sysdate), 2, 'deptno = 30');
1 row created.
SQL> create or replace function f_test return sys_refcursor
2 is
3 l_str varchar2(200);
4 l_rc sys_refcursor;
5 begin
6 select test_statement
7 into l_str
8 from test
9 where date_column = trunc(sysdate);
10
11 open l_rc for 'select deptno, ename from emp where ' || l_str;
12 return l_rc;
13 end;
14 /
Function created.
Testing:
SQL> select f_test from dual;
F_TEST
--------------------
CURSOR STATEMENT : 1
CURSOR STATEMENT : 1
DEPTNO ENAME
---------- ----------
30 ALLEN
30 WARD
30 MARTIN
30 BLAKE
30 TURNER
30 JAMES
6 rows selected.
SQL>
A good thing about it is that you could save the whole statements into that table and run any of them using the same function.

Answer 3

You can try this
select * from test_tab where mod(sysdate - date, frequency) = 0;