How to generate dynamic SQL statement with generic condition - oracle

Question

I am trying to generate a dynamic SQL statement with a generic condition.
Depending some conditions, it will be added different other conditions in where clause.
I was trying to have something like this:
declare
v_sql varchar2(500);
a number;
v_dummy number := 1;
begin
v_sql := 'delete tab_1 where v_dummy = 1 ';
if a = 1
then v_sql := v_sql || ' and col_1 = 1';
else v_sql := v_sql || ' and col_2 = 3';
end if;
execute immediate v_sql;
dbms_output.put_line(v_sql);
end;
The error raised is:
ORA-00904: "V_DUMMY": invalid identifier
Can anyone, please, guide me how to handle this situation?
The problem is with the definition of first condition (v_dummy = 1) that I need to add in order to use the "and" operand for the second condition.
Thank you,

Answer 1

If there is a possibility that you need multiple conditions (not in your code) you can set initial condition simply putting col_1 = col_1. No need for dummy variable at all and leaves you options to add some more conditions:
declare
v_sql varchar2(500);
a number;
begin
v_sql := 'delete tab_1 where col_1 = col_1 ';
if a = 1 then
v_sql := v_sql || ' and col_1 = 1';
else
v_sql := v_sql || ' and col_2 = 3';
end if;
execute immediate v_sql;
dbms_output.put_line(v_sql);
end;

Answer 2

Use a bind variable:
declare
v_sql varchar2(500);
a number;
v_dummy number := 1;
begin
v_sql := 'delete tab_1 where :v_dummy = 1 ';
if a = 1
then v_sql := v_sql || ' and col_1 = 1';
else v_sql := v_sql || ' and col_2 = 3';
end if;
execute immediate v_sql USING v_dummy;
dbms_output.put_line(v_sql);
end;
/
or since it evaluates to 1 = 1, you can omit it:
declare
v_sql varchar2(500);
a number;
begin
v_sql := 'delete tab_1';
if a = 1
then v_sql := v_sql || ' where col_1 = 1';
else v_sql := v_sql || ' where col_2 = 3';
end if;
execute immediate v_sql;
dbms_output.put_line(v_sql);
end;
/