Introduction to Oracle Cursors and Their Usage

2 years ago
Olivia Parker
2 minutes

The Oracle cursor is a type of database object used to process query result sets in PL/SQL programs. It is similar to a pointer and can iterate through each row of data in the result set.

Using a cursor can perform the following operations:

  1. Declare a cursor: Declare a cursor using the DECLARE statement, and specify the query statement.
  2. Open the cursor: Use the OPEN statement to execute the query and place the result set into the cursor.
  3. Retrieve data: use the FETCH statement to fetch one row of data from the cursor and store it in a variable.
  4. Data processing: manipulating, calculating, or otherwise handling the acquired data.
  5. Close cursor: Use the CLOSE statement to close the cursor.

Here is an example using a cursor:

DECLARE
  cursor_name CURSOR FOR SELECT column1, column2 FROM table_name;
  variable1 table_name.column1%TYPE;
  variable2 table_name.column2%TYPE;
BEGIN
  OPEN cursor_name;
  LOOP
    FETCH cursor_name INTO variable1, variable2;
    EXIT WHEN cursor_name%NOTFOUND;
    -- 处理数据，例如打印数据
    DBMS_OUTPUT.PUT_LINE('Column1: ' || variable1 || ', Column2: ' || variable2);
  END LOOP;
  CLOSE cursor_name;
END;

In the above example, a cursor called ‘cursor_name’ is first declared and a query is specified. Then, the cursor is opened using the OPEN statement, and data from the cursor is fetched line by line and stored in variables variable1 and variable2. The data is then processed in a loop until there is no more data in the cursor. Finally, the cursor is closed using the CLOSE statement.

Using cursors can handle large amounts of data more efficiently and allow for flexible manipulation of query result sets in PL/SQL programs.

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