python 连接postgres (3) - fetching results

psycopg2 commands

# conn = psycopg2.connect(...)
Establish a connection, starting a session, begins a transaction

# cursor = conn.cursor()
Sets a cursor to begin executing commands

# cursor.execute(<sql command string>)
# cursor.commit()  commit the transaction (not done automatically)
# cursor.rollback()   rollback the transaction

# cursor.fetchall()
# cursor.fetchmany(3)
# cursor.fetchone()   fetches the first result in the result set

# cursor.close()
# conn.close()   close the connection (not done automatically)

代码：

import psycopg2

# Establish the connection to our database
connection = psycopg2.connect('dbname=example')

# Working within session where we can start committing these transactions
# Queue up work into our transaction, we first have to start interacting with a cursor
# Cursor is basically an interface that allows you to start queuing up work and transactions. 
cursor = connection.cursor()

# cursor.execute immediately start executing work on the database.
# Create a transaction

cursor.execute('DROP TABLE IF EXISTS table2;')

cursor.execute('''
    CREATE TABLE table2 (
        id INTEGER PRIMARY KEY,
        completed BOOLEAN NOT NULL DEFAULT False
    );
''') 

# Use %s which turns this string into a template that we can then inject data in, 
cursor.execute('INSERT INTO table2 (id, completed) VALUES (%s, %s);', (1, True))


SQL = 'INSERT INTO table2 (id, completed) VALUES (%(id)s, %(completed)s);'
data = {
    
    
    'id': 2,
    'completed': False
}
cursor.execute(SQL, data)

# cursor.execute('INSERT INTO table2 (id, completed)' + ' VALUES (%(id)s, %(completed)s);',{
    
    
#     'id': 2,
#     'completed': False
# })

cursor.execute('INSERT INTO table2 (id, completed) VALUES (%s, %s);', (3, True))

cursor.execute('SELECT * from table2;')
result = cursor.fetchall()
print(result)

result2 = cursor.fetchone()
print(result2)

# Commit the work to the database
# connection.commite() will wound up committing both the create table and the insert into altogether. 
connection.commit()

# Clost the connection
# Psychopg2 will not automatically close out your connection for you. 
connection.close()
cursor.close()

运行上面的python， 结果如下：
[(1, True), (2, False), (3, True)]
None