What Identifier?
It’s always interesting to see students find the little nuances that SQL*Plus can generate. One of the first things we cover is the concept of calling PL/SQL interactively versus through an embedded call. The easiest and first exercise simply uses an insecure call like:
sqlplus -s student/student @call.sql |
to the call.sql
program:
SQL> DECLARE 2 lv_input VARCHAR2(20); 3 BEGIN 4 lv_input := '&1'; 5 dbms_output.put_line('['||lv_input||']'); 6 END; 7 / |
It prints the following to console:
Enter value for 1: machine old 4: lv_input := '&1'; new 4: lv_input := 'machine'; [machine] PL/SQL procedure successfully completed. |
Then, we change the '&1'
parameter variable to '&mystery'
and retest the program, which prints the following to the console:
Enter value for mystery: machine old 4: lv_input := '&mystery'; new 4: lv_input := 'machine'; [machine] PL/SQL procedure successfully completed. |
After showing a numeric and string input parameter, we remove the quotation from the lv_input
input parameter and raise the following error:
Enter value for mystery: machine old 4: lv_input := &mystery; new 4: lv_input := machine; lv_input := machine; * ERROR at line 4: ORA-06550: line 4, column 15: PLS-00201: identifier 'MACHINE' must be declared ORA-06550: line 4, column 3: PL/SQL: Statement ignored |
The point of the exercise is to spell out that the default input value is numeric and that if you pass a string it becomes an identifier in the scope of the program. So, we rewrite the call.sql
program file by adding a machine
variable, like:
SQL> DECLARE 2 lv_input VARCHAR2(20); 3 machine VARCHAR2(20) := 'Mystery Machine'; 4 BEGIN 5 lv_input := &mystery; 6 dbms_output.put_line('['||lv_input||']'); 7 END; 8 / |
It prints the following:
Enter value for mystery: machine old 5: lv_input := &mystery; new 5: lv_input := machine; [Mystery Machine] PL/SQL procedure successfully completed. |
The parameter name becomes an identifier and maps to the variable machine. That mapping means it prints the value of the machine
variable.
While this is what we’d call a terminal use case, it is a fun way to illustrate an odd PL/SQL behavior. As always, I hope its interesting for those who read it.