f you are not familiar with MySQL stored procedures or want to review it as a refresher, you can follow the MySQL stored procedures tutorial.
We will create two stored procedures for the demonstration in this tutorial. The first stored procedure gets all books with authors information from books and authors tables:
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DELIMITER $$
USE python_mysql$$
CREATE PROCEDURE find_all()
BEGIN
SELECT title, isbn, CONCAT(first_name,' ',last_name) AS author
FROM books
INNER JOIN book_author ON book_author.book_id = books.id
INNER JOIN AUTHORS ON book_author.author_id = authors.id;
END$$
DELIMITER ;
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The find_all() stored procedure has a SELECT statement with JOIN clauses that retrieve title, isbn and author’s full name from books and authors tables. When we execute the find_all() stored procedure, it returns a result as follows:
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CALL find_all();
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The second stored procedure named find_by_isbn() that is used to find a book by its ISBN as follows:
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DELIMITER $$
CREATE PROCEDURE find_by_isbn(IN p_isbn VARCHAR(13),OUT p_title VARCHAR(255))
BEGIN
SELECT title INTO p_title FROM books
WHERE isbn = p_isbn;
END$$
DELIMITER ;
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The find_by_isbn() accepts two parameters: the first parameter is isbn (IN parameter) and second is title (OUT parameter). When you pass the isbn to the stored procedure, you will get the title of the book, for example:
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CALL find_by_isbn('1235927658929',@title);
SELECT @title;
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Calling stored procedures from Python
To call a stored procedure in Python, you follow the steps below:
- Connect to MySQL database by creating a new MySQLConnection object.
- Instantiate a new MySQLCursor object from the MySQLConnection object by calling the cursor() method.
- Call
callproc()method of the MySQLCursor object. You pass the stored procedure’s name as the first argument of thecallproc()method. If the stored procedure requires parameters, you need to pass a list as the second argument to thecallproc()method. In case the stored procedure returns a result set, you can invoke thestored_results()method of the MySQLCursor object to get a list iterator and iterate this result set by using thefetchall()method. - Close the cursor and database connection as always.
The following example demonstrates how to call the find_all() stored procedure in Python and output the result set.
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from mysql.connector import MySQLConnection, Error
from python_mysql_dbconfig import read_db_config
def call_find_all_sp():
try:
db_config = read_db_config()
conn = MySQLConnection(**db_config)
cursor = conn.cursor()
cursor.callproc('find_all')
# print out the result
for result in cursor.stored_results():
print(result.fetchall())
except Error as e:
print(e)
finally:
cursor.close()
conn.close()
if __name__ == '__main__':
call_find_all_sp()
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The following example shows you how to call the find_by_isbn() stored procedure.
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from mysql.connector import MySQLConnection, Error
from python_mysql_dbconfig import read_db_config
def call_find_by_isbn():
try:
db_config = read_db_config()
conn = MySQLConnection(**db_config)
cursor = conn.cursor()
args = ['1236400967773', 0]
result_args = cursor.callproc('find_by_isbn', args)
print(result_args[1])
except Error as e:
print(e)
finally:
cursor.close()
conn.close()
if __name__ == '__main__':
call_find_by_isbn()
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The find_by_isbn() stored procedure requires two parameters therefore we have to pass a list ( args ) that contains two elements: the first one is isbn (1236400967773) and the second is 0. The second element of the args list (0) is just a placeholder to hold the p_title parameter.
The callproc() method returns a list ( result_args ) that contains two elements: the second element (result_args[1]) holds the value of the p_title parameter.
In this tutorial, we have shown you how to call stored procedures in Python by using callproc() method of the MySQLCursor object.
