Important Note: The cursor remains open until the end of transaction, and since PostgreSQL works in auto-commit mode by default, the cursor is closed immediately after the procedure call, so it is not available to the caller.To work with cursors the caller have to start a transaction.

• Postgresql Cursor Example
• Postgresql Cursor For Loop
• How To Create Cursor In Postgresql Example Pdf

Hello everyone, I'm a brand new person to postgreSql, but not for databases. I came from Oracle and Sybase areas. I'm struggling to create a stored procedure. I searched on Internet for several hours trying to find a simple example, but didn't find anything. I saw dozens of questions how to create a procedure without any responses. I searched on postgreSql site and found a topic 'Stored. 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: name NO SCROLL CURSOR ( arguments) FOR query. Implicit cursor. It's almost always better to use the implicit cursor of a FOR loop than to resort to a somewhat slower and unwieldy explicit cursor. I have written thousands of plpgsql functions and only a hand full of times explicit cursors made any sense.

Introduction to Cursors in PostgreSQL

If you’re writing code that interacts with PostgreSQL using Python or PHP, you’ll probably want to use cursors in your scripts. A PostgreSQL database cursor is a read-only pointer that allows a program, regardless of the language used, to access the result set of a query. This conserves the free memory of the server or machine running the SQL commands when a result set contains a large number of rows. Using cursors to iterate over rows of data also offers more control over the SQL records returned and makes the whole process more efficient. In this article, we’ll take a closer look at cursors and show you how to use a PostgreSQL cursor in Python, PHP and psql.

Cursors in Python using the PostgreSQL psycopg2 adapter

In Python, you can use the psycopg2 adapter for PostgreSQL to create cursors. A cursor can be created by calling the connection object’s cursor() method. Let’s look at an example where we instantiate a cursor and get its attributes:

NOTE: If you’re following along with this code example on your own machine, don’t forget to change the host parameters for the connect() method to match your PostgreSQL database’s settings.

When you pass the cursor instance to Python’s dir() function, it will return the following list of attributes:

You can get the cursor object’s type by passing it to Python’s type() function; it should return the following:

Execute a SQL query by calling the psycopg2 cursor object’s execute() method

The following block of Python code uses the cursor object’s execute() method to execute SQL commands to a PostgreSQL database:

Dell vostro 3550 wifi driver download. The code shown above uses the cursor object’s fetchall() method to return all of the table’s records in the form of a Python list.

Instantiate Cursors in PHP using the PDO() method

Now that we’ve looked at a Python example, let’s check out some PHP code. Here’s how to create a cursor pointer in PHP using the PDO (PHP Data Objects) interface to connect to PostgreSQL:

Create a new PDO connection to PostgreSQL in PHP

The following PHP code passes the cursor object to the print_r() method to print the SQL commands. After that, it creates a new connection to PostgreSQL using the PDO() method:

Use the PHP prepare() method to avoid SQL injection attacks

When you’re writing PHP code that interacts with a database, it’s important to add safeguards against SQL injection attacks. In the following block of code, we call the connection object’s beginTransaction() method to disable auto-commit. This ensures that changes to a table or database will not be in effect until the PDO commit() method is called:

NOTE: The connection’s prepare() method, which returns a statement object, is used to help prevent SQL injection attacks.

The following code prints some class attributes for the PDO statement object:

Prepare an inner statement for the SQL query and execute

In the next code snippet, we prepare a SQL query and execute the PDO statement. This enables the inner statement to prepare a response from the cursor:

Execute the PDO inner statement and fetch records from a PostgreSQL table

Next, let’s FETCH all of the records from the cursor object by passing a SQL statement to the connection object’s prepare() method. This will return a PDO inner statement object:

The code shown above executes the inner statement and prints the response. To test out this example on your own machine, simply save the PHP code in a script with the .php file extension, making sure the file is in your web root directory. Then, navigate to the file in a browser tab.

Create a CURSOR inside of the ‘psql’ interface for PostgreSQL

It’s also possible to create and use a PostgreSQL cursor in the psql interface. You can enter into the psql command-line interface for PostgreSQL by typing your username, domain host (-h), and PostgreSQL database (-d):

Once you’re connected, you can use the DECLARE keyword to create a new cursor for a table in the database:

DECLARE CURSOR can only be used in transaction blocks

If you don’t use the keyword WITH HOLD after declaring your cursor, you’ll get an error saying: DECLARE CURSOR can only be used in transaction blocks. This is because a cursor no longer exists after a transaction is called. It will be freed from the system’s memory unless you explicitly tell it not to.

To avoid this issue, simply use the WITH HOLD keywords before the SQL command:

After you execute this statement, you’ll get a response from PostgreSQL saying:

Conclusion

When you’re writing code that connects to PostgreSQL and executes queries, you want your interaction with the database to be as efficient as possible. Using cursors in your code can help you achieve this, allowing you to process queries with large result sets without maxing out your server’s free memory. In this article, we showed you how to create and use a PostgreSQL cursor in PHP, Python and psql. With all of these examples to guide you, you’ll be able to implement cursors in any of your database applications.

• PostgreSQL Tutorial

• Advanced PostgreSQL

• PostgreSQL Interfaces

• PostgreSQL Useful Resources

• Selected Reading

This chapter discusses about how to create a new database in your PostgreSQL. PostgreSQL provides two ways of creating a new database −

Postgresql Cursor Example

• Using CREATE DATABASE, an SQL command.
• Using createdb a command-line executable.

Using CREATE DATABASE

This command will create a database from PostgreSQL shell prompt, but you should have appropriate privilege to create a database. By default, the new database will be created by cloning the standard system database template1.

Syntax

The basic syntax of CREATE DATABASE statement is as follows −

where dbname is the name of a database to create.

Example

The following is a simple example, which will create testdb in your PostgreSQL schema

Using createdb Command

PostgreSQL command line executable createdb is a wrapper around the SQL command CREATE DATABASE. The only difference between this command and SQL command CREATE DATABASE is that the former can be directly run from the command line and it allows a comment to be added into the database, all in one command.

Syntax

The syntax for createdb is as shown below −

Parameters

The table given below lists the parameters with their descriptions.

Options

The following table lists the command line arguments createdb accepts −

Open the command prompt and go to the directory where PostgreSQL is installed. Go to the bin directory and execute the following command to create a database.

Postgresql Cursor For Loop

The above given command will prompt you for password of the PostgreSQL admin user, which is postgres, by default. Hence, provide a password and proceed to create your new database

How To Create Cursor In Postgresql Example Pdf

Once a database is created using either of the above-mentioned methods, you can check it in the list of databases using l, i.e., backslash el command as follows −