Oracle FAQS for PL/SQL developers

Can one print to the screen from PL/SQL?
One can use the DBMS_OUTPUT package to write information to an output buffer. This buffer can be displayed on the screen from SQL*Plus if you issue the SET SERVEROUTPUT ON; command. For example:
set serveroutput on
begin
dbms_output.put_line('Look Ma, I can print from PL/SQL!!!');
end;
/
DBMS_OUTPUT is useful for debugging PL/SQL programs. However, if you print too much, the output buffer will overflow. In that case, set the buffer size to a larger value, eg.: set serveroutput on size 200000
If you forget to set serveroutput on type SET SERVEROUTPUT ON once you remember, and then EXEC NULL;. If you haven't cleared the DBMS_OUTPUT buffer with the disable or enable procedure, SQL*Plus will display the entire contents of the buffer when it executes this dummy PL/SQL block.
Note that DBMS_OUTPUT doesn't print blank or NULL lines. To overcome this problem, SET SERVEROUTPUT ON FORMAT WRAP; Look at this example with this option first disabled and then enabled:
SQL> SET SERVEROUTPUT ON
SQL> begin
2 dbms_output.put_line('The next line is blank');
3 dbms_output.put_line();
4 dbms_output.put_line('The above line should be blank');
5 end;
6 /
The next line is blank
The above line should be blank
SQL> SET SERVEROUTPUT ON FORMAT WRAP
SQL> begin
2 dbms_output.put_line('The next line is blank');
3 dbms_output.put_line();
4 dbms_output.put_line('The above line should be blank');
5 end;
6 /
The next line is blank

The above line should be blank

Can one read/write files from PL/SQL?
The UTL_FILE database package can be used to read and write operating system files.
A DBA user needs to grant you access to read from/ write to a specific directory before using this package. Here is an example:
CONNECT / AS SYSDBA
CREATE OR REPLACE DIRECTORY mydir AS '/tmp';
GRANT read, write ON DIRECTORY mydir TO scott;
Provide user access to the UTL_FILE package (created by catproc.sql):
GRANT EXECUTE ON UTL_FILE TO scott;
Copy and paste these examples to get you started:
Write File
DECLARE
fHandler UTL_FILE.FILE_TYPE;
BEGIN
fHandler := UTL_FILE.FOPEN('MYDIR', 'myfile', 'w');
UTL_FILE.PUTF(fHandler, 'Look ma, Im writing to a file!!!\n');
UTL_FILE.FCLOSE(fHandler);
EXCEPTION
WHEN utl_file.invalid_path THEN
raise_application_error(-20000, 'Invalid path. Create directory or set UTL_FILE_DIR.');
END;
/
Read File
DECLARE
fHandler UTL_FILE.FILE_TYPE;
buf varchar2(4000);
BEGIN
fHandler := UTL_FILE.FOPEN('MYDIR', 'myfile', 'r');
UTL_FILE.GET_LINE(fHandler, buf);
dbms_output.put_line('DATA FROM FILE: 'buf);
UTL_FILE.FCLOSE(fHandler);
EXCEPTION
WHEN utl_file.invalid_path THEN
raise_application_error(-20000, 'Invalid path. Create directory or set UTL_FILE_DIR.');
END;
/
NOTE: UTL_FILE was introduced with Oracle 7.3. Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.

Can one call DDL statements from PL/SQL?
One can call DDL statements like CREATE, DROP, TRUNCATE, etc. from PL/SQL by using the "EXECUTE IMMEDIATE" statement (native SQL). Examples:
begin
EXECUTE IMMEDIATE 'CREATE TABLE X(A DATE)';
end;
begin execute Immediate 'TRUNCATE TABLE emp'; end;
DECLARE
var VARCHAR2(100);
BEGIN
var := 'CREATE TABLE temp1(col1 NUMBER(2))';
EXECUTE IMMEDIATE var;
END;
NOTE: The DDL statement in quotes should not be terminated with a semicolon.
Users running Oracle versions below Oracle 8i can look at the DBMS_SQL package (see FAQ about Dynamic SQL).
[edit]
Can one use dynamic SQL statements from PL/SQL?
Starting from Oracle8i one can use the "EXECUTE IMMEDIATE" statement to execute dynamic SQL and PL/SQL statements (statements created at run-time). Look at these examples. Note that the statements within quotes are NOT semicolon terminated:
EXECUTE IMMEDIATE 'CREATE TABLE x (a NUMBER)';

-- Using bind variables...'
sql_stmt := 'INSERT INTO dept VALUES (:1, :2, :3)';
EXECUTE IMMEDIATE sql_stmt USING dept_id, dept_name, location;

-- Returning a cursor...
sql_stmt := 'SELECT * FROM emp WHERE empno = :id';
EXECUTE IMMEDIATE sql_stmt INTO emp_rec USING emp_id;
One can also use the older DBMS_SQL package (V2.1 and above) to execute dynamic statements. Look at these examples:
CREATE OR REPLACE PROCEDURE DYNSQL AS
cur integer;
rc integer;
BEGIN
cur := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(cur, 'CREATE TABLE X (Y DATE)', DBMS_SQL.NATIVE);
rc := DBMS_SQL.EXECUTE(cur);
DBMS_SQL.CLOSE_CURSOR(cur);
END;
/
More complex DBMS_SQL example using bind variables:
CREATE OR REPLACE PROCEDURE DEPARTMENTS(NO IN DEPT.DEPTNO%TYPE) AS
v_cursor integer;
v_dname char(20);
v_rows integer;
BEGIN
v_cursor := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(v_cursor, 'select dname from dept where deptno > :x', DBMS_SQL.V7);
DBMS_SQL.BIND_VARIABLE(v_cursor, ':x', no);
DBMS_SQL.DEFINE_COLUMN_CHAR(v_cursor, 1, v_dname, 20);
v_rows := DBMS_SQL.EXECUTE(v_cursor);
loop
if DBMS_SQL.FETCH_ROWS(v_cursor) = 0 then
exit;
end if;
DBMS_SQL.COLUMN_VALUE_CHAR(v_cursor, 1, v_dname);
DBMS_OUTPUT.PUT_LINE('Deptartment name: 'v_dname);
end loop;
DBMS_SQL.CLOSE_CURSOR(v_cursor);
EXCEPTION
when others then
DBMS_SQL.CLOSE_CURSOR(v_cursor);
raise_application_error(-20000, 'Unknown Exception Raised: 'sqlcode' 'sqlerrm);
END;
/
What is the difference between %TYPE and %ROWTYPE?
Both %TYPE and %ROWTYPE are used to define variables in PL/SQL as it is defined within the database. If the datatype or precision of a column changes, the program automically picks up the new definition from the database without having to make any code changes.
The %TYPE and %ROWTYPE constructs provide data independence, reduces maintenance costs, and allows programs to adapt as the database changes to meet new business needs.
%TYPE
%TYPE is used to declare a field with the same type as that of a specified table's column. Example:
DECLARE
v_EmpName emp.ename%TYPE;
BEGIN
SELECT ename INTO v_EmpName FROM emp WHERE ROWNUM = 1;
DBMS_OUTPUT.PUT_LINE('Name = ' v_EmpName);
END;
/
%ROWTYPE
%ROWTYPE is used to declare a record with the same types as found in the specified database table, view or cursor. Examples:
DECLARE
v_emp emp%ROWTYPE;
BEGIN
v_emp.empno := 10;
v_emp.ename := 'XXXXXXX';
END;
/