PL/SQL Interview Questions
Describe the difference between a procedure, function and anonymous pl/sql
Candidate should mention use of DECLARE
statement, a function must return a value while a procedure doesn?t have to.
What is a mutating table error and how can you get around it?
This happens with triggers. It occurs because
the trigger is trying to update a row it is currently using. The usual fix
involves either use of views or temporary tables so the database is selecting
from one while updating the other.
Describe the use of %ROWTYPE and %TYPE in PL/SQL
Expected answer: %ROWTYPE allows you to
associate a variable with an entire table row. The %TYPE associates a variable
with a single column type.
4What packages (if any) has Oracle provided for use by developers?
Expected answer: Oracle provides the DBMS_
series of packages. There are many which developers should be aware of such as
DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT,
DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these
and describe how they used them, even better. If they include the SQL routines
provided by Oracle, great, but not really what was asked.
Describe the use of PL/SQL tables
Expected answer: PL/SQL tables are scalar arrays
that can be referenced by a binary integer. They can be used to hold values for
use in later queries or calculations. In Oracle 8 they will be able to be of the
%ROWTYPE designation, or RECORD.
When is a declare statement needed ?
The DECLARE statement is used in PL/SQL
anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must
come first in a PL/SQL stand alone file if it is used.
In what order should a open/fetch/loop set of commands in a PL/SQL block be
implemented if you use the %NOTFOUND cursor variable in the exit when statement?
Expected answer: OPEN then FETCH then LOOP
followed by the exit when. If not specified in this order will result in the
final return being done twice because of the way the %NOTFOUND is handled by
What are SQLCODE and SQLERRM and why are they important for PL/SQL
Expected answer: SQLCODE returns the value of
the error number for the last error encountered. The SQLERRM returns the actual
error message for the last error encountered. They can be used in exception
handling to report, or, store in an error log table, the error that occurred in
the code. These are especially useful for the WHEN OTHERS exception.
How can you find within a PL/SQL block, if a cursor is open?
Expected answer: Use the %ISOPEN cursor status
How can you generate debugging output from PL/SQL?
Expected answer: Use the DBMS_OUTPUT package.
Another possible method is to just use the SHOW ERROR command, but this only
shows errors. The DBMS_OUTPUT package can be used to show intermediate results
from loops and the status of variables as the procedure is executed. The new
package UTL_FILE can also be used.
What are the types of triggers?
Expected Answer: There are 12 types of triggers
in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT,
UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
AFTER INSERT etc.