Python MySQLDB: Get the result of fetchall in a list

问题

I would like to get the result of the fetchall operation in a list instead of tuple of tuple or tuple of dictionaries. For example,

cursor = connection.cursor() #Cursor could be a normal cursor or dict cursor
query = "Select id from bs"
cursor.execute(query)
row = cursor.fetchall()

Now, the problem is the resultant row is either ((123,),(234,)) or ({'id':123}, {'id':234}) What I am looking for is (123,234) or [123,234]. Be best if I can save on parsing the resulset. Thanks in advance

回答1:

And what about list comprehensions? If result is ((123,), (234,), (345,)):

>>> row = [item[0] for item in cursor.fetchall()]
>>> row
[123, 234, 345]

If result is ({'id': 123}, {'id': 234}, {'id': 345}):

>>> row = [item['id'] for item in cursor.fetchall()]
>>> row
[123, 234, 345]

回答2:

I'm sure that after all this time, you've solved this problem, however, for some people who may not know how to get the values of a cursor as a dictionary using MySQLdb, you can use this method found here:

import MySQLdb as mdb

con = mdb.connect('localhost', 'testuser', 'test623', 'testdb')

with con:

    cur = con.cursor(mdb.cursors.DictCursor)
    cur.execute("SELECT * FROM Writers LIMIT 4")

    rows = cur.fetchall()

    for row in rows:
        print row["Id"], row["Name"]

回答3:

This old Q comes up on Google while searching for flattening db queries, so here are more suggestions...

Consider a fast list-flattening iterator.

Others answers use fetchall() which first loads all rows in memory, then iterates over that to make a new list. Could be inefficient. Could combine with MySQL so-called server side cursor:

# assume mysql on localhost with db test and table bs
import itertools
import MySQLdb
import MySQLdb.cursors

conn = MySQLdb.connect(host='localhost',db='test', 
          cursorclass=MySQLdb.cursors.SSCursor ) 
cursor = conn.cursor()
# insert a bunch of rows
cursor.executemany('INSERT INTO bs (id) VALUES (%s)',zip(range(1,10000)) )
conn.commit()
# retrieve and listify
cursor.execute("select id from bs")
list_of_ids = list(itertools.chain.from_iterable(cursor))
len(list_of_ids)
#9999
conn.close()

But the question is also tagged Django, which has a nice single field query flattener

class Bs(models.Model):
    id_field = models.IntegerField()

list_of_ids = Bs.objects.values_list('id_field', flat=True)

回答4:

If there is only one field, i can use this to make a list from database:

def getFieldAsList():
    kursor.execute("Select id from bs")
    id_data = kursor.fetchall()
    id_list = []
    for index in range(len(id_data)):
        id_list.append(id_data[index][0])
    return id_list

回答5:

Make your cursor object in this manner:

db = MySQLdb.connect("IP", "user", "password", "dbname")

cursor = db.cursor(MySQLdb.cursors.DictCursor)

Then when you perform cursor.fetchall() on a query, a tuple of dictionaries will be obtained, which you can later convert to a list.

data = cursor.fetchall()

data = list(data)

回答6:

cursor.execute("""Select * From bs WHERE (id = %s)""",(id))

cursor.fetchall()

来源：https://stackoverflow.com/questions/12867140/python-mysqldb-get-the-result-of-fetchall-in-a-list

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python

django

mysql-python