What is the method for using PL/SQL cursors?

How to use PL/SQL cursors:

1. Declare a cursor: Use the DECLARE statement to declare a cursor, specify the cursor name and the returned result set.
2. Open the cursor: Use the OPEN statement to open the cursor and associate the cursor with the query statement.
3. Retrieve data: Use the FETCH statement to retrieve one row of data from the cursor and store it in a variable. Data can be stored in variables using the INTO clause.
4. Processing data: Handling the data returned in the loop. You can use LOOP, WHILE, or FOR statements to iterate through the result set returned by the cursor.
5. Close the cursor: Use the CLOSE statement to close the cursor and release the resources associated with it.
6. Handling exceptions: There may be exceptions that occur while using a cursor. EXCEPTION statements can be used to handle these exceptions.

Here is an example using a cursor:

DECLARE
  -- 声明游标
  CURSOR c_employee IS
    SELECT employee_id, first_name, last_name
    FROM employees;
  
  -- 声明变量
  v_employee_id employees.employee_id%TYPE;
  v_first_name employees.first_name%TYPE;
  v_last_name employees.last_name%TYPE;
BEGIN
  -- 打开游标
  OPEN c_employee;
  
  -- 循环处理数据
  LOOP
    -- 取回数据
    FETCH c_employee INTO v_employee_id, v_first_name, v_last_name;
    
    -- 判断是否还有数据
    EXIT WHEN c_employee%NOTFOUND;
    
    -- 处理数据
    DBMS_OUTPUT.PUT_LINE('Employee ID: ' || v_employee_id);
    DBMS_OUTPUT.PUT_LINE('First Name: ' || v_first_name);
    DBMS_OUTPUT.PUT_LINE('Last Name: ' || v_last_name);
    DBMS_OUTPUT.PUT_LINE('-------------------');
  END LOOP;
  
  -- 关闭游标
  CLOSE c_employee;
EXCEPTION
  -- 处理异常
  WHEN others THEN
    DBMS_OUTPUT.PUT_LINE('An error occurred: ' || SQLERRM);
    CLOSE c_employee;
END;

The above example demonstrates how to use a cursor to retrieve employee data from the employees table and print it to the output.