Oracle PL/SQL: Cursors

A cursor is a mechanism by which you can assign a name to a "select statement" and manipulate the information within that SQL statement.

Oracle PL/SQL: Declare a Cursor

A cursor is a SELECT statement that is defined within the declaration section of your PLSQL code. We’ll take a look at three different syntaxes for cursors.

Cursor without parameters (simplest)

The basic syntax for a cursor without parameters is:

CURSOR cursor_name
IS
    SELECT_statement;

For example, you could define a cursor called c1 as below.

CURSOR c1
IS
    SELECT course_number
      from courses_tbl
      where course_name = name_in;

The result set of this cursor is all course_numbers whose course_name matches the variable called name_in.

Below is a function that uses this cursor.

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    CURSOR c1
    IS
       SELECT course_number
        from courses_tbl
        where course_name = name_in;
BEGIN

open c1;
fetch c1 into cnumber;
if c1%notfound then
     cnumber := 9999;
end if;
close c1;

RETURN cnumber;

END;

Cursor with parameters

The basic syntax for a cursor with parameters is:

CURSOR cursor_name (parameter_list)
IS
    SELECT_statement;

For example, you could define a cursor called c2 as below.

CURSOR c2 (subject_id_in IN varchar2)
IS
    SELECT course_number
      from courses_tbl
      where subject_id = subject_id_in;

The result set of this cursor is all course_numbers whose subject_id matches the subject_id passed to the cursor via the parameter.

Cursor with return clause

The basic syntax for a cursor with a return clause is:

CURSOR cursor_name
RETURN field%ROWTYPE
IS
    SELECT_statement;

For example, you could define a cursor called c3 as below.

CURSOR c3
RETURN courses_tbl%ROWTYPE
IS
    SELECT *
      from courses_tbl
      where subject = ‘Mathematics’;

The result set of this cursor is all columns from the course_tbl where the subject is Mathematics.

Oracle PL/SQL: OPEN Statement

Once you’ve declared your cursor, the next step is to open the cursor.

The basic syntax to OPEN the cursor is:

OPEN cursor_name;

For example, you could open a cursor called c1 with the following command:

OPEN c1;

Below is a function that demonstrates how to use the OPEN statement:

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    CURSOR c1
    IS
       SELECT course_number
        from courses_tbl
        where course_name = name_in;
BEGIN

open c1;
fetch c1 into cnumber;
if c1%notfound then
     cnumber := 9999;
end if;
close c1;

RETURN cnumber;

END;

Oracle PL/SQL: FETCH Statement

The purpose of using a cursor, in most cases, is to retrieve the rows from your cursor so that some type of operation can be performed on the data. After declaring and opening your cursor, the next step is to FETCH the rows from your cursor.

The basic syntax for a FETCH statement is:

FETCH cursor_name INTO <list of variables>;

For example, you could have a cursor defined as:

CURSOR c1
IS
    SELECT course_number
      from courses_tbl
      where course_name = name_in;

The command that would be used to fetch the data from this cursor is:

FETCH c1 into cnumber;

This would fetch the first course_number into the variable called cnumber;

Below is a function that demonstrates how to use the FETCH statement.

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    CURSOR c1
    IS
       SELECT course_number
        from courses_tbl
        where course_name = name_in;
BEGIN

open c1;
fetch c1 into cnumber;
if c1%notfound then
     cnumber := 9999;
end if;
close c1;

RETURN cnumber;

END;

Oracle PL/SQL: CLOSE Statement

The final step of working with cursors is to close the cursor once you have finished using it.

The basic syntax to CLOSE the cursor is:

CLOSE cursor_name;

For example, you could close a cursor called c1 with the following command:

CLOSE c1;

Below is a function that demonstrates how to use the CLOSE statement:

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    CURSOR c1
    IS
       SELECT course_number
        from courses_tbl
        where course_name = name_in;
BEGIN

open c1;
fetch c1 into cnumber;
if c1%notfound then
     cnumber := 9999;
end if;
close c1;

RETURN cnumber;

END;

Related Posts

1. Oracle PL/SQL: Advanced Cursors
2. Oracle PL/SQL: Loops and Conditional Statements
3. Oracle PL/SQL: Primary keys
4. Inbuilt Functions in Oracle
5. Oracle PL/SQL: Is Null / Is Not Null

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