Question

Consider a table with 3 columns

Value1   operator     value2
abc          =               xyz
1            !=               2
5            >                8
9            <=              11
xyz          is not Null
{null val}   is null

I want to write a genric function which returns the validated result either true or false
by validating value1 with value2 using the operator
or check value1 in case of ‘is null’ and ‘is not null’ operators (Last two cases)

Answer 1

You could do something like this with dynamic SQL (note that in reality you’d need to add a bunch of logic to prevent SQL injection attacks)

SQL> ed
Wrote file afiedt.buf

  1  create or replace function evaluate( p_val1 in varchar2,
  2                                       p_op   in varchar2,
  3                                       p_val2 in varchar2 )
  4    return varchar2
  5  is
  6    l_result varchar2(1);
  7    l_sql_stmt varchar2(1000);
  8  begin
  9    if( p_val2 is not null )
 10    then
 11      l_sql_stmt := 'select (case when :1 ' || p_op || ' :2 then ''Y'' else ''N'' end) from dual';
 12      execute immediate l_sql_stmt
 13         into l_result
 14        using p_val1, p_val2;
 15    else
 16      l_sql_stmt := 'select (case when :1 ' || p_op || ' then ''Y'' else ''N'' end) from dual';
 17      execute immediate l_sql_stmt
 18         into l_result
 19        using p_val1;
 20    end if;
 21    return l_result;
 22* end;
SQL> /

Function created.

SQL>  select evaluate( 'xyz', 'is not null', null )
  2     from dual;

EVALUATE('XYZ','ISNOTNULL',NULL)
--------------------------------------------------------------------------------
Y

SQL> select evaluate( 'abc', '=', 'xyz' )
  2    from dual;

EVALUATE('ABC','=','XYZ')
--------------------------------------------------------------------------------
N

Since you are storing the data in a table, that implies that each column is a VARCHAR2. My guess, though, is that you don’t always want to use string comparison semantics. For example, the string ‘9’ is greater than the string ’11’ while the number 9 is less than the number 11. If you want to use something other than string comparison semantics, you’d need to add code that inspected the parameters and applied whatever logic you would like to determine what comparison semantics you want to apply and then generated the appropriate dynamic SQL statement.

I would strongly question the wisdom of the requirement, however. First off, it makes little sense from a data model standpoint to store numeric data in a VARCHAR2 column– when you find yourself trying to mix string and numeric data in the same column, you’ve almost always made a data model mistake. I would also be hard-pressed to imagine what business problem you are trying to solve that would involve this sort of dynamic function– it seems likely that there is a better way to solve whatever problem you are attempting to solve.