Oracle PL/SQL Tutorial/Cursor/ref cursor

Create and use reference cursor

SQL>
SQL> create table big_table as select * from all_objects;
Table created.
SQL>
SQL> declare
  2      c sys_refcursor;
  3      type array is table of big_table%rowtype index by binary_integer;
  4      l_rec array;
  5  begin
  6      for i in 1 .. 5
  7      loop
  8          open c for select * from big_table ORDER BY OWNER;
  9          fetch c bulk collect into l_rec limit i*1000;
 10          close c;
 11      end loop;
 12  end;
 13  /
PL/SQL procedure successfully completed.
SQL>
SQL> drop table big_table;
Table dropped.
SQL>

Creating a REF CURSOR datatype

The REF CURSOR datatype cannot be used outside a PL/SQL environment.

There are two kinds of REF CURSOR types: weak and strong.

A weak REF CURSOR can point to any data set, as shown here:

declare
  type weak_rcty is ref cursor;
  c_weak rcty weak_rcty;

REF CURSOR custom type

SQL> CREATE TABLE book (
  2    isbn      CHAR(10) PRIMARY KEY,
  3    category  VARCHAR2(20),
  4    title     VARCHAR2(100),
  5    num_pages NUMBER,
  6    price     NUMBER,
  7    copyright NUMBER(4),
  8    emp1   NUMBER,
  9    emp2   NUMBER,
 10    emp3   NUMBER
 11  );
Table created.
SQL>
SQL> INSERT INTO book (isbn, category, title, num_pages, price, copyright, emp1, emp2, emp3)
  2             VALUES ("1", "Database", "Oracle", 563, 39.99, 2009, 1, 2, 3);
1 row created.
SQL> INSERT INTO book (isbn, category, title, num_pages, price, copyright, emp1, emp2)
  2             VALUES ("2", "Database", "MySQL", 765, 44.99, 2009, 4, 5);
1 row created.
SQL> INSERT INTO book (isbn, category, title, num_pages, price, copyright, emp1, emp2, emp3)
  2             VALUES ("3", "Database", "SQL Server", 404, 39.99, 2001, 6, 7, 8);
1 row created.
SQL>
SQL>
SQL> SET SERVEROUTPUT ON ESCAPE OFF
SQL>
SQL> DECLARE
  2
  3     TYPE book_typ IS REF CURSOR RETURN book%ROWTYPE;
  4     cv_book book_typ;
  5     v_book book%ROWTYPE;
  6
  7  BEGIN
  8
  9     DBMS_OUTPUT.ENABLE(1000000);
 10
 11     OPEN cv_book FOR SELECT * FROM book WHERE isbn = "1";
 12
 13     FETCH cv_book INTO v_book;
 14
 15     DBMS_OUTPUT.PUT_LINE(v_book.title||" is "||v_book.price);
 16
 17     CLOSE cv_book;
 18  END;
 19  /
Oracle is 39.99
PL/SQL procedure successfully completed.
SQL>
SQL> drop table book;
Table dropped.

Reference cursor

SQL>
SQL> CREATE TABLE emp (
  2    id         NUMBER PRIMARY KEY,
  3    fname VARCHAR2(50),
  4    lname  VARCHAR2(50)
  5  );
Table created.
SQL>
SQL> INSERT INTO emp (id, fname, lname)VALUES (1, "A", "B");
1 row created.
SQL> INSERT INTO emp (id, fname, lname)VALUES (2, "C", "D");
1 row created.
SQL> INSERT INTO emp (id, fname, lname)VALUES (3, "Enn", "F");
1 row created.
SQL> INSERT INTO emp (id, fname, lname)VALUES (4, "G", "H");
1 row created.
SQL> INSERT INTO emp (id, fname, lname)VALUES (5, "G", "Z");
1 row created.
SQL>
SQL>
SQL> SET SERVEROUTPUT ON ESCAPE OFF
SQL>
SQL> CREATE OR REPLACE PROCEDURE emp_sel (cv_results IN OUT SYS_REFCURSOR)
  2  IS
  3  BEGIN
  4     OPEN cv_results FOR SELECT id, fname, lname FROM emp;
  5  END;
  6  /
Procedure created.
SQL>
SQL> VARIABLE x REFCURSOR
SQL>
SQL> EXEC emp_sel(:x)
PL/SQL procedure successfully completed.
SQL>
SQL> print x
        ID FNAME
---------- --------------------------------------------------
LNAME
--------------------------------------------------
         1 A
B
         2 C
D
         3 Enn
F
         4 G
H
         5 G
Z

5 rows selected.
SQL>
SQL> drop table emp;
Table dropped.
SQL>

Reference value in a cursor by cursor variable

SQL>
SQL> -- create demo table
SQL> create table emp(
  2    ID                 VARCHAR2(4 BYTE)         NOT NULL,
  3    fname         VARCHAR2(10 BYTE),
  4    lname          VARCHAR2(10 BYTE),
  5    Start_Date         DATE,
  6    End_Date           DATE,
  7    Salary             Number(8,2),
  8    City               VARCHAR2(10 BYTE),
  9    Description        VARCHAR2(15 BYTE)
 10  )
 11  /
Table created.
SQL>
SQL> -- prepare data
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2               values ("01","Jason",    "Martin",  to_date("19960725","YYYYMMDD"), to_date("20060725","YYYYMMDD"), 1234.56, "Toronto",  "Programmer")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("02","Alison",   "Mathews", to_date("19760321","YYYYMMDD"), to_date("19860221","YYYYMMDD"), 6661.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("03","James",    "Smith",   to_date("19781212","YYYYMMDD"), to_date("19900315","YYYYMMDD"), 6544.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("04","Celia",    "Rice",    to_date("19821024","YYYYMMDD"), to_date("19990421","YYYYMMDD"), 2344.78, "Vancouver","Manager")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("05","Robert",   "Black",   to_date("19840115","YYYYMMDD"), to_date("19980808","YYYYMMDD"), 2334.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("06","Linda",    "Green",   to_date("19870730","YYYYMMDD"), to_date("19960104","YYYYMMDD"), 4322.78,"New York",  "Tester")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("07","David",    "Larry",   to_date("19901231","YYYYMMDD"), to_date("19980212","YYYYMMDD"), 7897.78,"New York",  "Manager")
  3  /
1 row created.
SQL> insert into emp(ID,  fname, lname, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("08","James",    "Cat",     to_date("19960917","YYYYMMDD"), to_date("20020415","YYYYMMDD"), 1232.78,"Vancouver", "Tester")
  3  /
1 row created.
SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from emp
  2  /
ID   FNAME      LNAME      START_DAT END_DATE      SALARY CITY
---- ---------- ---------- --------- --------- ---------- ----------
DESCRIPTION
---------------
01   Jason      Martin     25-JUL-96 25-JUL-06    1234.56 Toronto
Programmer
02   Alison     Mathews    21-MAR-76 21-FEB-86    6661.78 Vancouver
Tester
03   James      Smith      12-DEC-78 15-MAR-90    6544.78 Vancouver
Tester

ID   FNAME      LNAME      START_DAT END_DATE      SALARY CITY
---- ---------- ---------- --------- --------- ---------- ----------
DESCRIPTION
---------------
04   Celia      Rice       24-OCT-82 21-APR-99    2344.78 Vancouver
Manager
05   Robert     Black      15-JAN-84 08-AUG-98    2334.78 Vancouver
Tester
06   Linda      Green      30-JUL-87 04-JAN-96    4322.78 New York
Tester

ID   FNAME      LNAME      START_DAT END_DATE      SALARY CITY
---- ---------- ---------- --------- --------- ---------- ----------
DESCRIPTION
---------------
07   David      Larry      31-DEC-90 12-FEB-98    7897.78 New York
Manager
08   James      Cat        17-SEP-96 15-APR-02    1232.78 Vancouver
Tester

8 rows selected.

SQL> CREATE OR REPLACE PROCEDURE myProcedure
  2  AS
  3      CURSOR myCursor IS SELECT id, fname FROM emp;
  4      TYPE firstNameType IS TABLE OF emp.fname%type INDEX BY emp.id%type;
  5      ch firstNameType;
  6      i integer := 0;
  7      imax integer;
  8  BEGIN
  9    FOR j IN myCursor LOOP
 10      i := i + 1;
 11      ch(i) := j.fname;
 12    END LOOP;
 13    dbms_output.put_line(ch("James"));
 14  END myProcedure;
 15  /
Procedure created.
SQL>
SQL> exec myProcedure;
SQL>
SQL>
SQL>
SQL> -- clean the table
SQL> drop table emp
  2  /
Table dropped.
SQL>
SQL>
SQL>

Timing a ref cursor

SQL>
SQL> declare
  2      type rc is ref cursor;
  3      l_rc rc;
  4      l_dummy all_objects.object_name%type;
  5      l_start number default dbms_utility.get_time;
  6  begin
  7      for i in 1 .. 1000
  8      loop
  9          open l_rc for
 10          "select object_name
 11             from all_objects
 12            where object_id = :x"
 13          using i;
 14          fetch l_rc into l_dummy;
 15          close l_rc;
 16      end loop;
 17      dbms_output.put_line
 18      ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
 19        " seconds..." );
 20  end;
 21  /
.63 seconds...
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.70
SQL>
SQL> set timing off