Bulk update MySql with python

Question

I have to update millions of row into MySQL. I am currently using for loop to execute query. To make the update faster I want to use executemany() of Python MySQL Connector, so that I can update in batches using single query for each batch.

Answer 1

I don't think mysqldb has a way of handling multiple UPDATE queries at one time.

But you can use an INSERT query with ON DUPLICATE KEY UPDATE condition at the end.

I written the following example for ease of use and readability.

import MySQLdb

def update_many(data_list=None, mysql_table=None):
    """
    Updates a mysql table with the data provided. If the key is not unique, the
    data will be inserted into the table.

    The dictionaries must have all the same keys due to how the query is built.

    Param:
        data_list (List):
            A list of dictionaries where the keys are the mysql table
            column names, and the values are the update values
        mysql_table (String):
            The mysql table to be updated.
    """

    # Connection and Cursor
    conn = MySQLdb.connect('localhost', 'jeff', 'atwood', 'stackoverflow')
    cur = conn.cursor()

    query = ""
    values = []

    for data_dict in data_list:

        if not query:
            columns = ', '.join('`{0}`'.format(k) for k in data_dict)
            duplicates = ', '.join('{0}=VALUES({0})'.format(k) for k in data_dict)
            place_holders = ', '.join('%s'.format(k) for k in data_dict)
            query = "INSERT INTO {0} ({1}) VALUES ({2})".format(mysql_table, columns, place_holders)
            query = "{0} ON DUPLICATE KEY UPDATE {1}".format(query, duplicates)

        v = data_dict.values()
        values.append(v)

    try:
        cur.executemany(query, values)
    except MySQLdb.Error, e:
        try:
            print"MySQL Error [%d]: %s" % (e.args[0], e.args[1])
        except IndexError:
            print "MySQL Error: %s" % str(e)

        conn.rollback()
        return False

    conn.commit()
    cur.close()
    conn.close()

Explanation of one liners

columns = ', '.join('`{}`'.format(k) for k in data_dict)

is the same as

column_list = []
for k in data_dict:
    column_list.append(k)
columns = ", ".join(columns)

Here's an example of usage

test_data_list = []
test_data_list.append( {'id' : 1, 'name' : 'Marco', 'articles' : 1 } )
test_data_list.append( {'id' : 2, 'name' : 'Keshaw', 'articles' : 8 } )
test_data_list.append( {'id' : 3, 'name' : 'Wes', 'articles' : 0 } )

update_many(data_list=test_data_list, mysql_table='writers')

Query output

INSERT INTO writers (`articles`, `id`, `name`) VALUES (%s, %s, %s) ON DUPLICATE KEY UPDATE articles=VALUES(articles), id=VALUES(id), name=VALUES(name)

Values output

[[1, 1, 'Marco'], [8, 2, 'Keshaw'], [0, 3, 'Wes']]