问题
Im using Aqua Data Studio to debug a stored proc by scattering output statments throughout.
I have a delete statement in the package which violate an integrity constraint:
DELETE FROM x WHERE x.ID = an_x_with_children;
My proc fails with an ORA-02292 on this line, as expected. I want to see the value of the an_x_with_children variable. So I wrap the line with outputs like so:
dbms_output.put('Attempting to delete x: ' || an_x_with_children);
DELETE FROM x WHERE x.ID = an_x_with_children;
dbms_output.put(' Success');
And expect to see the message as the last thing in the messages console prior to the integrity constraint violated error message. But it doesn't print!
Now if I change the output to use the put_line() procedure like this:
dbms_output.put_line('Attempting to delete x: ' || an_x_with_children);
DELETE FROM x WHERE x.ID = an_x_with_children;
dbms_output.put_line(' Success');
I see the message "Attempting to delete x: 123" immediately before the proc errors out.
The docs for the dbms_output package don't mention the put and put_line procedures behaving any differently in this respect. For instance, it says
Output that you create using PUT or PUT_LINE is buffered.
So I would expect either both or neither to show output when the proc errors.
Can someone explain what's going on with this behaviour to me?
回答1:
Here is an example that shows the behaviour you're seeing:
SQL> exec dbms_output.put_line('hello')
hello
PL/SQL procedure successfully completed.
SQL> exec dbms_output.put('hello again')
PL/SQL procedure successfully completed.
SQL> exec dbms_output.put(' and again')
PL/SQL procedure successfully completed.
SQL> exec dbms_output.new_line
hello again and again
PL/SQL procedure successfully completed.
The documentation says "SQL*Plus calls GET_LINES after issuing a SQL statement or anonymous PL/SQL calls."
And procedure GET_LINES says "This procedure retrieves an array of lines from the buffer."
With PUT you haven't completed your line yet. And so it doesn't print.
The NEW_LINE procedure mentions this as well: "This procedure puts an end-of-line marker. The GET_LINE Procedure and the GET_LINES Procedure return "lines" as delimited by "newlines". Every call to the PUT_LINE Procedure or NEW_LINE Procedure generates a line that is returned by GET_LINE(S)."
Regards,
Rob.
来源：https://stackoverflow.com/questions/12532211/is-dbms-output-put-being-buffered-differently-from-dbms-output-put-line