- As of PostgreSQL 7.1.x, cursors may only be defined as READ ONLY, and the FOR clause is therefore superfluous. Example 7-42 begins a transaction block with the BEGIN keyword, and opens a cursor named allbooks with SELECT. FROM books as its executed SQL statement.
- Declaring Cursor Variables. All access to cursors in PL/pgSQL goes through cursor variables, which are always of the special data type refcursor.One way to create a cursor variable is just to declare it as a variable of type refcursor.Another way is to use the cursor declaration syntax, which in general is.
Examples (these use the cursor declaration examples above): OPEN curs2; OPEN curs3(42); OPEN curs3(key:= 42); Because variable substitution is done on a bound cursor's query, there are really two ways to pass values into the cursor: either with an explicit argument to OPEN, or implicitly by referencing a PL/pgSQL variable in the query.
- Related Questions & Answers
- Selected Reading
In this tutorial, we are going to learn how to use PostgreSQL with Python. You have to install certain thing before going into the tutorial. Let's install them.
Install the PostgreSQL with the guide.
Install the Python module psycopg2 for PostgreSQL connection and working. Run the command to install it.
Now, open the pgAdmin. And create a sample database. Next, follow the below steps to get started with database operations.
- Import the psycopg2 module.
- Store the database name, username, and password in separate variables.
- Make a connection to the database using psycopg2.connect(database=name,user=name, password=password) method.
- Instantiate a cursor object to execute SQL commands.
- Create queries and execute them with cursor.execute(query) method.
- And get the information using cursor.fetchall() method if available.
- Close the connection using connection.close() method.
Example
Output
If you run the above code, then you will get the following result.
Conclusion
If you have any doubts in the tutorial, mention them in the comment section.
Summary: in this tutorial, you will learn how to use the PL/SQL cursor FOR LOOP statement to fetch and process every record from a cursor.
Introduction to PL/SQL cursor FOR LOOP statement
The cursor FOR LOOP statement is an elegant extension of the numeric FOR LOOP statement.
The numeric FOR LOOP executes the body of a loop once for every integer value in a specified range. Similarly, the cursor FOR LOOP executes the body of the loop once for each row returned by the query associated with the cursor.
A nice feature of the cursor FOR LOOP statement is that it allows you to fetch every row from a cursor without manually managing the execution cycle i.e., OPEN, FETCH, and CLOSE.
The cursor FOR LOOP implicitly creates its loop index as a record variable with the row type in which the cursor returns and then opens the cursor.
In each loop iteration, the cursor FOR LOOP statement fetches a row from the result set into its loop index. If there is no row to fetch, the cursor FOR LOOP closes the cursor.
The cursor is also closed if a statement inside the loop transfers control outside the loop, e.g., EXIT and GOTO, or raises an exception.
The following illustrates the syntax of the cursor FOR LOOP statement:
1) record
The record is the name of the index that the cursor FOR LOOP statement declares implicitly as a %ROWTYPE record variable of the type of the cursor.
The record variable is local to the cursor FOR LOOP statement. It means that you can only reference it inside the loop, not outside. After the cursor FOR LOOP statement execution ends, the record variable becomes undefined.
2) cursor_name
The cursor_name is the name of an explicit cursor that is not opened when the loop starts.
New installation of s 4hana 1610. Note that besides the cursor name, you can use a SELECT statement as shown below:
Postgresql Cursor Example Image
In this case, the cursor FOR LOOP declares, opens, fetches from, and closes an implicit cursor. However, the implicit cursor is internal; therefore, you cannot reference it.
Oracle Cursor For Update Example
Note that Oracle Database automatically optimizes a cursor FOR LOOP to work similarly to a BULK COLLECT query. Although your code looks as if it fetched one row at a time, Oracle Database fetches multiple rows at a time and allows you to process each row individually.
PL/SQL cursor FOR LOOP examples
Let's look at some examples of using the cursor FOR LOOP statement to see how it works.
A) PL/SQL cursor FOR LOOP example
Install the Python module psycopg2 for PostgreSQL connection and working. Run the command to install it.
Now, open the pgAdmin. And create a sample database. Next, follow the below steps to get started with database operations.
- Import the psycopg2 module.
- Store the database name, username, and password in separate variables.
- Make a connection to the database using psycopg2.connect(database=name,user=name, password=password) method.
- Instantiate a cursor object to execute SQL commands.
- Create queries and execute them with cursor.execute(query) method.
- And get the information using cursor.fetchall() method if available.
- Close the connection using connection.close() method.
Example
Output
If you run the above code, then you will get the following result.
Conclusion
If you have any doubts in the tutorial, mention them in the comment section.
Summary: in this tutorial, you will learn how to use the PL/SQL cursor FOR LOOP statement to fetch and process every record from a cursor.
Introduction to PL/SQL cursor FOR LOOP statement
The cursor FOR LOOP statement is an elegant extension of the numeric FOR LOOP statement.
The numeric FOR LOOP executes the body of a loop once for every integer value in a specified range. Similarly, the cursor FOR LOOP executes the body of the loop once for each row returned by the query associated with the cursor.
A nice feature of the cursor FOR LOOP statement is that it allows you to fetch every row from a cursor without manually managing the execution cycle i.e., OPEN, FETCH, and CLOSE.
The cursor FOR LOOP implicitly creates its loop index as a record variable with the row type in which the cursor returns and then opens the cursor.
In each loop iteration, the cursor FOR LOOP statement fetches a row from the result set into its loop index. If there is no row to fetch, the cursor FOR LOOP closes the cursor.
The cursor is also closed if a statement inside the loop transfers control outside the loop, e.g., EXIT and GOTO, or raises an exception.
The following illustrates the syntax of the cursor FOR LOOP statement:
1) record
The record is the name of the index that the cursor FOR LOOP statement declares implicitly as a %ROWTYPE record variable of the type of the cursor.
The record variable is local to the cursor FOR LOOP statement. It means that you can only reference it inside the loop, not outside. After the cursor FOR LOOP statement execution ends, the record variable becomes undefined.
2) cursor_name
The cursor_name is the name of an explicit cursor that is not opened when the loop starts.
New installation of s 4hana 1610. Note that besides the cursor name, you can use a SELECT statement as shown below:
Postgresql Cursor Example Image
In this case, the cursor FOR LOOP declares, opens, fetches from, and closes an implicit cursor. However, the implicit cursor is internal; therefore, you cannot reference it.
Oracle Cursor For Update Example
Note that Oracle Database automatically optimizes a cursor FOR LOOP to work similarly to a BULK COLLECT query. Although your code looks as if it fetched one row at a time, Oracle Database fetches multiple rows at a time and allows you to process each row individually.
PL/SQL cursor FOR LOOP examples
Let's look at some examples of using the cursor FOR LOOP statement to see how it works.
A) PL/SQL cursor FOR LOOP example
The following example declares an explicit cursor and uses it in the cursor FOR LOOP statement.
In this example, the SELECT statement of the cursor retrieves data from the products table. The FOR LOOP statement opened, fetched each row in the result set, displayed the product information, and closed the cursor.
Postgresql Cursor Example Key
B) Cursor FOR LOOP with a SELECT statement example
The following example is equivalent to the example above but uses a query in a cursor FOR LOOP statement.
In this tutorial, you have learned how to use the PL/SQL cursor FOR LOOP to fetch data from a cursor.
