Python3 MySQL database
Python3 uses PyMySQL to connect to the database and implement simple addition, deletion, modification and query.
What is PyMySQL?
PyMySQL is a library for connecting to MySQL servers in Python 3.x, and mysqldb in Python 2.
PyMySQL follows the Python Database API v2.0 specification and includes the pure-Python MySQL client library.
PyMySQL installation
Before using PyMySQL, we need to make sure that PyMySQL is installed.
PyMySQL download address: https://github.com/PyMySQL/PyMySQL.
If it is not already installed, we can install the latest version of PyMySQL with the following command:
$ pip install PyMySQL
If your system does not support the pip command, you can install it using:
1. Use the git command to download the installation package and install (you can also download it manually):
$ git clone https://github.com/PyMySQL/PyMySQL $ cd PyMySQL/ $ python3 setup.py install
2. If you need to specify the version number, you can use the curl command to install:
$ # XX is the version number of PyMySQL $ curl -L https://github.com/PyMySQL/PyMySQL/tarball/pymysql-XX | tar xz $ cd PyMySQL* $ python3 setup.py install $ # Now you can delete the PyMySQL* directory
Note: Make sure you have root privileges to install the above modules.
During the installation process, the error message "ImportError: No module named setuptools" may appear, which means that you do not have setuptools installed. You can visit https://pypi.python.org/pypi/setuptools to find the installation method for each system.
Linux system installation example:
$ wget https://bootstrap.pypa.io/ez_setup.py
$ python3 ez_setup.py
Database linkage
Before connecting to the database, please confirm the following:
- You have created the database TESTDB.
- In the TESTDB database you have created the table EMPLOYEE
- The EMPLOYEE table fields are FIRST_NAME, LAST_NAME, AGE, SEX and INCOME.
- The user name used to connect to the database TESTDB is "testuser" and the password is "test123". You can set it yourself or use the root user name and password directly. For Mysql database user authorization, use the Grant command.
- The Python MySQLdb module has been installed on your machine.
Example:
The following example links the Mysql TESTDB database:
Example (Python 3.0+)
#!/usr/bin/python3 import pymysql #Open database connection db = pymysql.connect ( " localhost " , " testuser " , " test123 " , " TESTDB " ) #Use the cursor() method to create a cursor object cursor cursor = db.cursor() #Use the execute() method to execute the SQL query cursor.execute( " SELECT VERSION() " ) #Use the fetchone() method to get a single piece of data. data = cursor.fetchone() print ("Database version : %s " % data) #Close the database connection db.close()
The output of executing the above script is as follows:
Database version : 5.5.20-log
Create database table
If the database connection exists we can use the execute() method to create a table for the database, as follows to create the table EMPLOYEE:
Example (Python 3.0+)
#!/usr/bin/python3 import pymysql #Open database connection db = pymysql.connect ( " localhost " , " testuser " , " test123 " , " TESTDB " ) #Use the cursor() method to create a cursor object cursor cursor = db.cursor() #Use the execute() method to execute SQL, if the table exists, delete cursor.execute( " DROP TABLE IF EXISTS EMPLOYEE " ) #Create table using prepared statements sql = """ CREATE TABLE EMPLOYEE ( FIRST_NAME CHAR(20) NOT NULL, LAST_NAME CHAR(20), AGE INT, SEX CHAR(1), INCOME FLOAT )""" cursor.execute(sql) #Close the database connection db.close()
database insert operation
The following example inserts records into table EMPLOYEE using the execute SQL INSERT statement:
Example (Python 3.0+)
#!/usr/bin/python3 import pymysql #Open database connection db = pymysql.connect ( " localhost " , " testuser " , " test123 " , " TESTDB " ) #Use the cursor() method to get the operation cursor cursor = db.cursor() # SQL insert statement sql = """ INSERT INTO EMPLOYEE(FIRST_NAME, LAST_NAME, AGE, SEX, INCOME) VALUES ('Mac', 'Mohan', 20, 'M', 2000) """ try : #Execute the sql statement cursor.execute(sql) #Submit to the database and execute db.commit() except : #If an error occurs, then rollback db.rollback() #Close the database connection db.close()
The above example can also be written as:
Example (Python 3.0+)
#!/usr/bin/python3 import pymysql #Open database connection db = pymysql.connect ( " localhost " , " testuser " , " test123 " , " TESTDB " ) #Use the cursor() method to get the operation cursor cursor = db.cursor() # SQL insert statement sql = " INSERT INTO EMPLOYEE(FIRST_NAME, \ LAST_NAME, AGE, SEX, INCOME) \ VALUES ('%s', '%s', '%d', '%c', '%d' )" % \ ( ' Mac ' , ' Mohan ' , 20, ' M ' , 2000 ) try : #Execute the sql statement cursor.execute(sql) #Execute the sql statement db.commit() except : #rollback when an error occurs db.rollback( ) #Close the database connection db.close()
The following code uses variables to pass parameters into the SQL statement:
.................................. user_id = "test123" password = "password" con.execute('insert into Login values("%s", "%s")' % \ (user_id, password)) ..................................
Database query operation
The Python query Mysql uses the fetchone() method to obtain a single piece of data, and the fetchall() method to obtain multiple pieces of data.
- fetchone(): This method fetches the next query result set. The result set is an object
- fetchall(): Receives all returned result rows.
- rowcount: This is a read-only property and returns the number of rows affected by executing the execute() method.
Example:
Query all data in the salary field greater than 1000 in the EMPLOYEE table:
Example (Python 3.0+)
#!/usr/bin/python3 import pymysql #Open database connection db = pymysql.connect ( " localhost " , " testuser " , " test123 " , " TESTDB " ) #Use the cursor() method to get the operation cursor cursor = db.cursor() # SQL query statement sql = " SELECT * FROM EMPLOYEE \ WHERE INCOME > '%d' " % (1000 ) try : #Execute the SQL statement cursor.execute(sql) #Get a list of all records results = cursor.fetchall() for row in results: fname = row[0] lname = row[1] age = row[2] sex = row[3] income = row[4] # 打印结果 print ("fname=%s,lname=%s,age=%d,sex=%s,income=%d" % \ (fname, lname, age, sex, income )) except: print ("Error: unable to fetch data") #Close the database connection db.close()
The result of executing the above script is as follows:
fname=Mac, lname=Mohan, age=20, sex=M, income=2000
database update operation
The update operation is used to update the data of the data table. The following example modifies all the SEX fields in the TESTDB table to 'M' and increments the AGE field by 1: