Question

Can I change the value of a variable by using a select into with the variable’s original value as part of the where clause in the select statement?

EI would the following code work as expected:

declare
v_id number;
v_table number; --set elsewhere in code to either 1 or 2
begin
  select id into v_id from table_1 where name = 'John Smith';
  if(v_table = 2) then
    select id into v_id from table_2 where fk_id = v_id;
  end if;
end;

Answer 1

Should work. Have you tried it? Any issues?

After parsing your select statements should have bind variables where your v_id is. The substitution is made when the statement is actually executed.

Edit:
Unless you’re sticking constants into your queries, Oracle will always parse them into statements with bind variables – it enables the DBMS to reuse the same basic query with multiple values without reparsing the statement – a huge performance gain. The whole idea of a bind variable is runtime substitution of values into a parsed query. Think of it this way: in order to process a query, all of the values need to be known. You send them to the engine, Oracle does it’s work, and returns a result. It’s a serial process with no way for the output value to step on the input one.