Category: python Postgresql

Python PostgreSQL – Cursor Object ”; Previous Next The Cursor class of the psycopg library provide methods to execute the PostgreSQL commands in the database using python code. Using the methods of it you can execute SQL statements, fetch data from the result sets, call procedures. You can create Cursor object using the cursor() method of the Connection object/class. Example import psycopg2 #establishing the connection conn = psycopg2.connect( database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() Methods Following are the various methods provided by the Cursor class/object. Sr.No. Methods & Description 1 callproc() This method is used to call existing procedures PostgreSQL database. 2 close() This method is used to close the current cursor object. 3 executemany() This method accepts a list series of parameters list. Prepares an MySQL query and executes it with all the parameters. 4 execute() This method accepts a MySQL query as a parameter and executes the given query. 5 fetchall() This method retrieves all the rows in the result set of a query and returns them as list of tuples. (If we execute this after retrieving few rows it returns the remaining ones) 6 fetchone() This method fetches the next row in the result of a query and returns it as a tuple. 7 fetchmany() This method is similar to the fetchone() but, it retrieves the next set of rows in the result set of a query, instead of a single row. Properties Following are the properties of the Cursor class − Sr.No. Property & Description 1 description This is a read only property which returns the list containing the description of columns in a result-set. 2 lastrowid This is a read only property, if there are any auto-incremented columns in the table, this returns the value generated for that column in the last INSERT or, UPDATE operation. 3 rowcount This returns the number of rows returned/updated in case of SELECT and UPDATE operations. 4 closed This property specifies whether a cursor is closed or not, if so it returns true, else false. 5 connection This returns a reference to the connection object using which this cursor was created. 6 name This property returns the name of the cursor. 7 scrollable This property specifies whether a particular cursor is scrollable. Print Page Previous Next Advertisements ”;

Python PostgreSQL – Useful Resources ”; Previous Next The following resources contain additional information on Python PostgreSQL. Please use them to get more in-depth knowledge on this. Useful Video Courses Python Flask and SQLAlchemy ORM 22 Lectures 1.5 hours Jack Chan More Detail Python and Elixir Programming Bundle Course 81 Lectures 9.5 hours Pranjal Srivastava More Detail TKinter Course – Build Python GUI Apps 49 Lectures 4 hours John Elder More Detail A Beginner”s Guide to Python and Data Science 81 Lectures 8.5 hours Datai Team Academy More Detail Deploy Face Recognition Project With Python, Django, And Machine Learning Best Seller 93 Lectures 6.5 hours Srikanth Guskra More Detail Professional Python Web Development with Flask 80 Lectures 12 hours Stone River ELearning More Detail Print Page Previous Next Advertisements ”;

Discuss Python PostgreSQL ”; Previous Next Python is a general-purpose interpreted, interactive, object-oriented, and high-level programming language. It was created by Guido van Rossum during 1985-1990. Like Perl, Python source code is also available under the GNU General Public License (GPL). This tutorial gives enough understanding on Python programming language. This tutorial explains how to communicate with PostgreSQL database in detail, along with examples. Print Page Previous Next Advertisements ”;

Python PostgreSQL – Quick Guide ”; Previous Next Python PostgreSQL – Introduction PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development phase and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness. To communicate with PostgreSQL using Python you need to install psycopg, an adapter provided for python programming, the current version of this is psycog2. psycopg2 was written with the aim of being very small and fast, and stable as a rock. It is available under PIP (package manager of python) Installing Psycog2 using PIP First of all, make sure python and PIP is installed in your system properly and, PIP is up-to-date. To upgrade PIP, open command prompt and execute the following command − C:UsersTutorialspoint>python -m pip install –upgrade pip Collecting pip Using cached https://files.pythonhosted.org/packages/8d/07/f7d7ced2f97ca3098c16565efbe6b15fafcba53e8d9bdb431e09140514b0/pip-19.2.2-py2.py3-none-any.whl Installing collected packages: pip Found existing installation: pip 19.0.3 Uninstalling pip-19.0.3: Successfully uninstalled pip-19.0.3 Successfully installed pip-19.2.2 Then, open command prompt in admin mode and execute the pip install psycopg2-binary command as shown below − C:WINDOWSsystem32>pip install psycopg2-binary Collecting psycopg2-binary Using cached https://files.pythonhosted.org/packages/80/79/d0d13ce4c2f1addf4786f4a2ded802c2df66ddf3c1b1a982ed8d4cb9fc6d/psycopg2_binary-2.8.3-cp37-cp37m-win32.whl Installing collected packages: psycopg2-binary Successfully installed psycopg2-binary-2.8.3 Verification To verify the installation, create a sample python script with the following line in it. import mysql.connector If the installation is successful, when you execute it, you should not get any errors − D:Python_PostgreSQL>import psycopg2 D:Python_PostgreSQL> Python PostgreSQL – Database Connection PostgreSQL provides its own shell to execute queries. To establish connection with the PostgreSQL database, make sure that you have installed it properly in your system. Open the PostgreSQL shell prompt and pass details like Server, Database, username, and password. If all the details you have given are appropriate, a connection is established with PostgreSQL database. While passing the details you can go with the default server, database, port and, user name suggested by the shell. Establishing Connection Using Python The connection class of the psycopg2 represents/handles an instance of a connection. You can create new connections using the connect() function. This accepts the basic connection parameters such as dbname, user, password, host, port and returns a connection object. Using this function, you can establish a connection with the PostgreSQL. Example The following Python code shows how to connect to an existing database. If the database does not exist, then it will be created and finally a database object will be returned. The name of the default database of PostgreSQL is postrgre. Therefore, we are supplying it as the database name. import psycopg2 #establishing the connection conn = psycopg2.connect( database=”postgres”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Creating a cursor object using the cursor() method cursor = conn.cursor() #Executing an MYSQL function using the execute() method cursor.execute(“select version()”) #Fetch a single row using fetchone() method. data = cursor.fetchone() print(“Connection established to: “,data) #Closing the connection conn.close() Connection established to: ( ”PostgreSQL 11.5, compiled by Visual C++ build 1914, 64-bit”, ) Output Connection established to: ( ”PostgreSQL 11.5, compiled by Visual C++ build 1914, 64-bit”, ) Python PostgreSQL – Create Database You can create a database in PostgreSQL using the CREATE DATABASE statement. You can execute this statement in PostgreSQL shell prompt by specifying the name of the database to be created after the command. Syntax Following is the syntax of the CREATE DATABASE statement. CREATE DATABASE dbname; Example Following statement creates a database named testdb in PostgreSQL. postgres=# CREATE DATABASE testdb; CREATE DATABASE You can list out the database in PostgreSQL using the l command. If you verify the list of databases, you can find the newly created database as follows − postgres=# l List of databases Name | Owner | Encoding | Collate | Ctype | ———–+———-+———-+—————————-+————-+ mydb | postgres | UTF8 | English_United States.1252 | ……….. | postgres | postgres | UTF8 | English_United States.1252 | ……….. | template0 | postgres | UTF8 | English_United States.1252 | ……….. | template1 | postgres | UTF8 | English_United States.1252 | ……….. | testdb | postgres | UTF8 | English_United States.1252 | ……….. | (5 rows) You can also create a database in PostgreSQL from command prompt using the command createdb, a wrapper around the SQL statement CREATE DATABASE. C:Program FilesPostgreSQL11bin> createdb -h localhost -p 5432 -U postgres sampledb Password: Creating a Database Using Python The cursor class of psycopg2 provides various methods execute various PostgreSQL commands, fetch records and copy data. You can create a cursor object using the cursor() method of the Connection class. The execute() method of this class accepts a PostgreSQL query as a parameter and executes it. Therefore, to create a database in PostgreSQL, execute the CREATE DATABASE query using this method. Example Following python example creates a database named mydb in PostgreSQL database. import psycopg2 #establishing the connection conn = psycopg2.connect( database=”postgres”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Preparing query to create a database sql = ”””CREATE database mydb”””; #Creating a database cursor.execute(sql) print(“Database created successfully……..”) #Closing the connection conn.close() Output Database created successfully…….. Python PostgreSQL – Create Table You can create a new table in a database in PostgreSQL using the CREATE TABLE statement. While executing this you need to specify the name of the table, column names and their data types. Syntax Following is the syntax of the CREATE TABLE statement in PostgreSQL. CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, ….. columnN datatype, ); Example Following example creates a table with name CRICKETERS in PostgreSQL.

Python PostgreSQL – Order By ”; Previous Next Usually if you try to retrieve data from a table, you will get the records in the same order in which you have inserted them. Using the ORDER BY clause, while retrieving the records of a table you can sort the resultant records in ascending or descending order based on the desired column. Syntax Following is the syntax of the ORDER BY clause in PostgreSQL. SELECT column-list FROM table_name [WHERE condition] [ORDER BY column1, column2, .. columnN] [ASC | DESC]; Example Assume we have created a table with name CRICKETERS using the following query − postgres=# CREATE TABLE CRICKETERS ( First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, Place_Of_Birth VARCHAR(255), Country VARCHAR(255) ); CREATE TABLE postgres=# And if we have inserted 5 records in to it using INSERT statements as − postgres=# insert into CRICKETERS values(”Shikhar”, ”Dhawan”, 33, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values(”Jonathan”, ”Trott”, 38, ”CapeTown”, ”SouthAfrica”); INSERT 0 1 postgres=# insert into CRICKETERS values(”Kumara”, ”Sangakkara”, 41, ”Matale”, ”Srilanka”); INSERT 0 1 postgres=# insert into CRICKETERS values(”Virat”, ”Kohli”, 30, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values(”Rohit”, ”Sharma”, 32, ”Nagpur”, ”India”); INSERT 0 1 Following SELECT statement retrieves the rows of the CRICKETERS table in the ascending order of their age − postgres=# SELECT * FROM CRICKETERS ORDER BY AGE; first_name | last_name | age | place_of_birth | country ————+————+—–+—————-+————- Virat | Kohli | 30 | Delhi | India Rohit | Sharma | 32 | Nagpur | India Shikhar | Dhawan | 33 | Delhi | India Jonathan | Trott | 38 | CapeTown | SouthAfrica Kumara | Sangakkara | 41 | Matale | Srilanka (5 rows)es: You can use more than one column to sort the records of a table. Following SELECT statements sort the records of the CRICKETERS table based on the columns age and FIRST_NAME. postgres=# SELECT * FROM CRICKETERS ORDER BY AGE, FIRST_NAME; first_name | last_name | age | place_of_birth | country ————+————+—–+—————-+————- Virat | Kohli | 30 | Delhi | India Rohit | Sharma | 32 | Nagpur | India Shikhar | Dhawan | 33 | Delhi | India Jonathan | Trott | 38 | CapeTown | SouthAfrica Kumara | Sangakkara | 41 | Matale | Srilanka (5 rows) By default, the ORDER BY clause sorts the records of a table in ascending order. You can arrange the results in descending order using DESC as − postgres=# SELECT * FROM CRICKETERS ORDER BY AGE DESC; first_name | last_name | age | place_of_birth | country ————+————+—–+—————-+————- Kumara | Sangakkara | 41 | Matale | Srilanka Jonathan | Trott | 38 | CapeTown | SouthAfrica Shikhar | Dhawan | 33 | Delhi | India Rohit | Sharma | 32 | Nagpur | India Virat | Kohli | 30 | Delhi | India (5 rows) ORDER BY Clause Using Python To retrieve contents of a table in specific order, invoke the execute() method on the cursor object and, pass the SELECT statement along with ORDER BY clause, as a parameter to it. Example In the following example, we are creating a table with name and Employee, populating it, and retrieving its records back in the (ascending) order of their age, using the ORDER BY clause. import psycopg2 #establishing the connection conn = psycopg2.connect( database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Doping EMPLOYEE table if already exists. cursor.execute(“DROP TABLE IF EXISTS EMPLOYEE”) #Creating a table sql = ”””CREATE TABLE EMPLOYEE( FIRST_NAME CHAR(20) NOT NULL, LAST_NAME CHAR(20), AGE INT, SEX CHAR(1), INCOME INT, CONTACT INT)””” cursor.execute(sql) #Populating the table insert_stmt = “INSERT INTO EMPLOYEE (FIRST_NAME, LAST_NAME, AGE, SEX, INCOME, CONTACT) VALUES (%s, %s, %s, %s, %s, %s)” data = [(”Krishna”, ”Sharma”, 26, ”M”, 2000, 101), (”Raj”, ”Kandukuri”, 20, ”M”, 7000, 102), (”Ramya”, ”Ramapriya”, 29, ”F”, 5000, 103), (”Mac”, ”Mohan”, 26, ”M”, 2000, 104)] cursor.executemany(insert_stmt, data) conn.commit() #Retrieving specific records using the ORDER BY clause cursor.execute(“SELECT * from EMPLOYEE ORDER BY AGE”) print(cursor.fetchall()) #Commit your changes in the database conn.commit() #Closing the connection conn.close() Output [(”Sharukh”, ”Sheik”, 25, ”M”, 8300.0), (”Sarmista”, ”Sharma”, 26, ”F”, 10000.0)] Print Page Previous Next Advertisements ”;

Python PostgreSQL – Delete Data ”; Previous Next You can delete the records in an existing table using the DELETE FROM statement of PostgreSQL database. To remove specific records, you need to use WHERE clause along with it. Syntax Following is the syntax of the DELETE query in PostgreSQL − DELETE FROM table_name [WHERE Clause] Example Assume we have created a table with name CRICKETERS using the following query − postgres=# CREATE TABLE CRICKETERS ( First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, Place_Of_Birth VARCHAR(255), Country VARCHAR(255) ); CREATE TABLE postgres=# And if we have inserted 5 records in to it using INSERT statements as − postgres=# insert into CRICKETERS values (”Shikhar”, ”Dhawan”, 33, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Jonathan”, ”Trott”, 38, ”CapeTown”, ”SouthAfrica”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Kumara”, ”Sangakkara”, 41, ”Matale”, ”Srilanka”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Virat”, ”Kohli”, 30, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Rohit”, ”Sharma”, 32, ”Nagpur”, ”India”); INSERT 0 1 Following statement deletes the record of the cricketer whose last name is ”Sangakkara”. postgres=# DELETE FROM CRICKETERS WHERE LAST_NAME = ”Sangakkara”; DELETE 1 If you retrieve the contents of the table using the SELECT statement, you can see only 4 records since we have deleted one. postgres=# SELECT * FROM CRICKETERS; first_name | last_name | age | place_of_birth | country ————+———–+—–+—————-+————- Jonathan | Trott | 39 | CapeTown | SouthAfrica Virat | Kohli | 31 | Delhi | India Rohit | Sharma | 33 | Nagpur | India Shikhar | Dhawan | 46 | Delhi | India (4 rows) If you execute the DELETE FROM statement without the WHERE clause all the records from the specified table will be deleted. postgres=# DELETE FROM CRICKETERS; DELETE 4 Since you have deleted all the records, if you try to retrieve the contents of the CRICKETERS table, using SELECT statement you will get an empty result set as shown below − postgres=# SELECT * FROM CRICKETERS; first_name | last_name | age | place_of_birth | country ————+———–+—–+—————-+——— (0 rows) Deleting Data Using Python The cursor class of psycopg2 provides a method with name execute() method. This method accepts the query as a parameter and executes it. Therefore, to insert data into a table in PostgreSQL using python − Import psycopg2 package. Create a connection object using the connect() method, by passing the user name, password, host (optional default: localhost) and, database (optional) as parameters to it. Turn off the auto-commit mode by setting false as value to the attribute autocommit. The cursor() method of the Connection class of the psycopg2 library returns a cursor object. Create a cursor object using this method. Then, execute the DELETE statement by passing it as a parameter to the execute() method. Example Following Python code deletes records of the EMPLOYEE table with age values greater than 25 − import psycopg2 #establishing the connection conn = psycopg2.connect( database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Retrieving contents of the table print(“Contents of the table: “) cursor.execute(”””SELECT * from EMPLOYEE”””) print(cursor.fetchall()) #Deleting records cursor.execute(”””DELETE FROM EMPLOYEE WHERE AGE > 25”””) #Retrieving data after delete print(“Contents of the table after delete operation “) cursor.execute(“SELECT * from EMPLOYEE”) print(cursor.fetchall()) #Commit your changes in the database conn.commit() #Closing the connection conn.close() Output Contents of the table: [ (”Ramya”, ”Rama priya”, 27, ”F”, 9000.0), (”Sarmista”, ”Sharma”, 26, ”F”, 10000.0), (”Tripthi”, ”Mishra”, 24, ”F”, 6000.0), (”Vinay”, ”Battacharya”, 21, ”M”, 6000.0), (”Sharukh”, ”Sheik”, 26, ”M”, 8300.0) ] Contents of the table after delete operation: [ (”Tripthi”, ”Mishra”, 24, ”F”, 6000.0), (”Vinay”, ”Battacharya”, 21, ”M”, 6000.0) ] Print Page Previous Next Advertisements ”;

Python PostgreSQL – Join ”; Previous Next When you have divided the data in two tables you can fetch combined records from these two tables using Joins. Example Assume we have created a table with name CRICKETERS and inserted 5 records into it as shown below − postgres=# CREATE TABLE CRICKETERS ( First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, Place_Of_Birth VARCHAR(255), Country VARCHAR(255) ); postgres=# insert into CRICKETERS values (”Shikhar”, ”Dhawan”, 33, ”Delhi”, ”India”); postgres=# insert into CRICKETERS values (”Jonathan”, ”Trott”, 38, ”CapeTown”, ”SouthAfrica”); postgres=# insert into CRICKETERS values (”Kumara”, ”Sangakkara”, 41, ”Matale”, ”Srilanka”); postgres=# insert into CRICKETERS values (”Virat”, ”Kohli”, 30, ”Delhi”, ”India”); postgres=# insert into CRICKETERS values (”Rohit”, ”Sharma”, 32, ”Nagpur”, ”India”); And, if we have created another table with name OdiStats and inserted 5 records into it as − postgres=# CREATE TABLE ODIStats ( First_Name VARCHAR(255), Matches INT, Runs INT, AVG FLOAT, Centuries INT, HalfCenturies INT ); postgres=# insert into OdiStats values (”Shikhar”, 133, 5518, 44.5, 17, 27); postgres=# insert into OdiStats values (”Jonathan”, 68, 2819, 51.25, 4, 22); postgres=# insert into OdiStats values (”Kumara”, 404, 14234, 41.99, 25, 93); postgres=# insert into OdiStats values (”Virat”, 239, 11520, 60.31, 43, 54); postgres=# insert into OdiStats values (”Rohit”, 218, 8686, 48.53, 24, 42); Following statement retrieves data combining the values in these two tables − postgres=# SELECT Cricketers.First_Name, Cricketers.Last_Name, Cricketers.Country, OdiStats.matches, OdiStats.runs, OdiStats.centuries, OdiStats.halfcenturies from Cricketers INNER JOIN OdiStats ON Cricketers.First_Name = OdiStats.First_Name; first_name | last_name | country | matches | runs | centuries | halfcenturies ————+————+————-+———+——-+———–+————— Shikhar | Dhawan | India | 133 | 5518 | 17 | 27 Jonathan | Trott | SouthAfrica | 68 | 2819 | 4 | 22 Kumara | Sangakkara | Srilanka | 404 | 14234 | 25 | 93 Virat | Kohli | India | 239 | 11520 | 43 | 54 Rohit | Sharma | India | 218 | 8686 | 24 | 42 (5 rows) postgres=# Joins Using Python When you have divided the data in two tables you can fetch combined records from these two tables using Joins. Example Following python program demonstrates the usage of the JOIN clause − import psycopg2 #establishing the connection conn = psycopg2.connect( database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Retrieving single row sql = ”””SELECT * from EMP INNER JOIN CONTACT ON EMP.CONTACT = CONTACT.ID””” #Executing the query cursor.execute(sql) #Fetching 1st row from the table result = cursor.fetchall(); print(result) #Commit your changes in the database conn.commit() #Closing the connection conn.close() Output [ (”Ramya”, ”Rama priya”, 27, ”F”, 9000.0, 101, 101, ”[email protected]”, ”Hyderabad”), (”Vinay”, ”Battacharya”, 20, ”M”, 6000.0, 102, 102, ”[email protected]”, ”Vishakhapatnam”), (”Sharukh”, ”Sheik”, 25, ”M”, 8300.0, 103, 103, ”[email protected] ”, ”Pune”), (”Sarmista”, ”Sharma”, 26, ”F”, 10000.0, 104, 104, ”[email protected]”, ”Mumbai”) ] Print Page Previous Next Advertisements ”;

Python PostgreSQL – Limit ”; Previous Next While executing a PostgreSQL SELECT statement you can limit the number of records in its result using the LIMIT clause. Syntax Following is the syntax of the LMIT clause in PostgreSQL − SELECT column1, column2, columnN FROM table_name LIMIT [no of rows] Example Assume we have created a table with name CRICKETERS using the following query − postgres=# CREATE TABLE CRICKETERS ( First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, Place_Of_Birth VARCHAR(255), Country VARCHAR(255) ); CREATE TABLE postgres=# And if we have inserted 5 records in to it using INSERT statements as − postgres=# insert into CRICKETERS values (”Shikhar”, ”Dhawan”, 33, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Jonathan”, ”Trott”, 38, ”CapeTown”, ”SouthAfrica”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Kumara”, ”Sangakkara”, 41, ”Matale”, ”Srilanka”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Virat”, ”Kohli”, 30, ”Delhi”, ”India”); INSERT 0 1 postgres=# insert into CRICKETERS values (”Rohit”, ”Sharma”, 32, ”Nagpur”, ”India”); INSERT 0 1 Following statement retrieves the first 3 records of the Cricketers table using the LIMIT clause − postgres=# SELECT * FROM CRICKETERS LIMIT 3; first_name | last_name | age | place_of_birth | country ————+————+—–+—————-+————- Shikhar | Dhawan | 33 | Delhi | India Jonathan | Trott | 38 | CapeTown | SouthAfrica Kumara | Sangakkara | 41 | Matale | Srilanka (3 rows) If you want to get records starting from a particular record (offset) you can do so, using the OFFSET clause along with LIMIT. postgres=# SELECT * FROM CRICKETERS LIMIT 3 OFFSET 2; first_name | last_name | age | place_of_birth | country ————+————+—–+—————-+———- Kumara | Sangakkara | 41 | Matale | Srilanka Virat | Kohli | 30 | Delhi | India Rohit | Sharma | 32 | Nagpur | India (3 rows) postgres=# Limit Clause Using Python Following python example retrieves the contents of a table named EMPLOYEE, limiting the number of records in the result to 2 − import psycopg2 #establishing the connection conn = psycopg2.connect( database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Retrieving single row sql = ”””SELECT * from EMPLOYEE LIMIT 2 OFFSET 2””” #Executing the query cursor.execute(sql) #Fetching the data result = cursor.fetchall(); print(result) #Commit your changes in the database conn.commit() #Closing the connection conn.close() Output [(”Sharukh”, ”Sheik”, 25, ”M”, 8300.0), (”Sarmista”, ”Sharma”, 26, ”F”, 10000.0)] Print Page Previous Next Advertisements ”;

Python PostgreSQL – Drop Table ”; Previous Next You can drop a table from PostgreSQL database using the DROP TABLE statement. Syntax Following is the syntax of the DROP TABLE statement in PostgreSQL − DROP TABLE table_name; Example Assume we have created two tables with name CRICKETERS and EMPLOYEES using the following queries − postgres=# CREATE TABLE CRICKETERS ( First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, Place_Of_Birth VARCHAR(255), Country VARCHAR(255) ); CREATE TABLE postgres=# postgres=# CREATE TABLE EMPLOYEE( FIRST_NAME CHAR(20) NOT NULL, LAST_NAME CHAR(20), AGE INT, SEX CHAR(1), INCOME FLOAT ); CREATE TABLE postgres=# Now if you verify the list of tables using the “dt” command, you can see the above created tables as − postgres=# dt; List of relations Schema | Name | Type | Owner ——–+————+——-+———- public | cricketers | table | postgres public | employee | table | postgres (2 rows) postgres=# Following statement deletes the table named Employee from the database − postgres=# DROP table employee; DROP TABLE Since you have deleted the Employee table, if you retrieve the list of tables again, you can observe only one table in it. postgres=# dt; List of relations Schema | Name | Type | Owner ——–+————+——-+———- public | cricketers | table | postgres (1 row) postgres=# If you try to delete the Employee table again, since you have already deleted it, you will get an error saying “table does not exist” as shown below − postgres=# DROP table employee; ERROR: table “employee” does not exist postgres=# To resolve this, you can use the IF EXISTS clause along with the DELTE statement. This removes the table if it exists else skips the DLETE operation. postgres=# DROP table IF EXISTS employee; NOTICE: table “employee” does not exist, skipping DROP TABLE postgres=# Removing an Entire Table Using Python You can drop a table whenever you need to, using the DROP statement. But you need to be very careful while deleting any existing table because the data lost will not be recovered after deleting a table. import psycopg2 #establishing the connection conn = psycopg2.connect(database=”mydb”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432”) #Setting auto commit false conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Doping EMPLOYEE table if already exists cursor.execute(“DROP TABLE emp”) print(“Table dropped… “) #Commit your changes in the database conn.commit() #Closing the connection conn.close() Output #Table dropped… Print Page Previous Next Advertisements ”;

Python PostgreSQL – Create Database ”; Previous Next You can create a database in PostgreSQL using the CREATE DATABASE statement. You can execute this statement in PostgreSQL shell prompt by specifying the name of the database to be created after the command. Syntax Following is the syntax of the CREATE DATABASE statement. CREATE DATABASE dbname; Example Following statement creates a database named testdb in PostgreSQL. postgres=# CREATE DATABASE testdb; CREATE DATABASE You can list out the database in PostgreSQL using the l command. If you verify the list of databases, you can find the newly created database as follows − postgres=# l List of databases Name | Owner | Encoding | Collate | Ctype | ———–+———-+———-+—————————-+————-+ mydb | postgres | UTF8 | English_United States.1252 | ……….. | postgres | postgres | UTF8 | English_United States.1252 | ……….. | template0 | postgres | UTF8 | English_United States.1252 | ……….. | template1 | postgres | UTF8 | English_United States.1252 | ……….. | testdb | postgres | UTF8 | English_United States.1252 | ……….. | (5 rows) You can also create a database in PostgreSQL from command prompt using the command createdb, a wrapper around the SQL statement CREATE DATABASE. C:Program FilesPostgreSQL11bin> createdb -h localhost -p 5432 -U postgres sampledb Password: Creating a Database Using Python The cursor class of psycopg2 provides various methods execute various PostgreSQL commands, fetch records and copy data. You can create a cursor object using the cursor() method of the Connection class. The execute() method of this class accepts a PostgreSQL query as a parameter and executes it. Therefore, to create a database in PostgreSQL, execute the CREATE DATABASE query using this method. Example Following python example creates a database named mydb in PostgreSQL database. import psycopg2 #establishing the connection conn = psycopg2.connect( database=”postgres”, user=”postgres”, password=”password”, host=”127.0.0.1”, port= ”5432” ) conn.autocommit = True #Creating a cursor object using the cursor() method cursor = conn.cursor() #Preparing query to create a database sql = ”””CREATE database mydb”””; #Creating a database cursor.execute(sql) print(“Database created successfully……..”) #Closing the connection conn.close() Output Database created successfully…….. Print Page Previous Next Advertisements ”;