You use a cursor when you have a SELECT statement that returns more than one row from the database.
A cursor is basically a set of rows that you can access one at a time.
You retrieve the rows into the cursor using your SELECT statement and then fetch the rows from the cursor.
You may follow five steps when using a cursor:
- Declare variables to store the column values from the SELECT statement.
- Declare the cursor, specifying your SELECT statement.
- Open the cursor.
- Fetch the rows from the cursor.
- Close the cursor.
The syntax for declaring a cursor is as follows:
CURSOR cursor_name IS
SELECT_statement;
where
cursor_name specifies the name of the cursor.
SELECT_statement is a SELECT statement.
You open a cursor using the OPEN statement, which must be placed in the executable section of the block.
To read each row from the cursor, you can use the FETCH statement.
The FETCH statement reads the column values into the variables that you specify;
FETCH uses the following syntax:
FETCH cursor_name
INTO variable[, variable ...];
where
- cursor_name specifies the name of the cursor.
- variable is a previously declared variable into which values from the cursor's SELECT statement are stored.
Once you've finished with the cursor, the final step is to close the cursor using the CLOSE statement.
Closing your cursors frees up system resources.
SQL>
SQL>
SQL> -- create demo table
SQL> create table Employee(
2 ID VARCHAR2(4 BYTE) NOT NULL primary key,
3 First_Name VARCHAR2(10 BYTE),
4 Last_Name 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee(ID, First_Name, Last_Name, 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 Employee
2 /
ID FIRST_NAME LAST_NAME 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
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
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>
SQL>
SQL>
SQL>
SQL> SET SERVEROUTPUT ON
SQL> DECLARE
2 -- step 1: declare the variables
3 v_id employee. id%TYPE;
4 v_name employee.first_name%TYPE;
5 v_salary employee.salary%TYPE;
6
7 -- step 2: declare the cursor
8 CURSOR cv_employee_cursor IS
9 SELECT id, first_name, salary
10 FROM employee
11 ORDER BY id;
12
13 BEGIN
14
15 -- step 3: open the cursor
16 OPEN cv_employee_cursor;
17
18 LOOP
19
20 -- step 4: fetch the rows from the cursor
21 FETCH cv_employee_cursor
22 INTO v_id, v_name, v_salary;
23
24 -- exit the loop when there are no more rows, as indicated by
25 -- the Boolean variable NOTFOUND (= true when
26 -- there are no more rows)
27 EXIT WHEN cv_employee_cursor%NOTFOUND;
28 -- use DBMS_OUTPUT.PUT_LINE() to display the variables
29 DBMS_OUTPUT.PUT_LINE(
30 'v_id = ' || v_id || ', v_name = ' || v_name ||
31 ', v_salary = ' || v_salary
32 );
33
34 END LOOP;
35
36 -- step 5: close the cursor
37 CLOSE cv_employee_cursor;
38
39 END;
40 /
v_id = 01, v_name = Jason, v_salary = 1234.56
v_id = 02, v_name = Alison, v_salary = 6661.78
v_id = 03, v_name = James, v_salary = 6544.78
v_id = 04, v_name = Celia, v_salary = 2344.78
v_id = 05, v_name = Robert, v_salary = 2334.78
v_id = 06, v_name = Linda, v_salary = 4322.78
v_id = 07, v_name = David, v_salary = 7897.78
v_id = 08, v_name = James, v_salary = 1232.78
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
2 /
Table dropped.