python

Question

为什么 presto timestamp/decimal(38,18) 数据类型返回一个字符串（包含在 u'' 中）而不是 python datetime/numeric 类型？

急速 jdbc:

select 来自 hive.x.y

的 typeof(col1),typeof(col2),typeof(col3),typeof(col4),typeof(col5),typeof(col6)

结果是

timestamp timestamp bigint decimal(38,18) varchar varchar

desc hive.x.y
#result is
for_dt  timestamp   NO  NO  NO  NO  1
for_d   timestamp   NO  NO  NO  NO  2
for_h   bigint  NO  NO  NO  NO  3
value   decimal(38,18)  NO  NO  NO  NO  4
metric  varchar(2147483647) NO  NO  NO  NO  5
lat_lon varchar(2147483647) NO  NO  NO  NO  6

attempt 1
#python
from sqlalchemy.engine import create_engine
engine = create_engine('presto://u:p@host:port',connect_args={'protocol': 'https', 'requests_kwargs': {'verify': 'mypem'}})
result = engine.execute('select * from hive.x.y limit 1')
print(result.fetchall())
#result is
[(u'2010-02-18 03:00:00.000', u'2010-02-18 00:00:00.000', 3, u'-0.191912651062011660', u'hey', u'there')]

attempt 2
#python
from pyhive import presto
import requests
from requests.auth import HTTPBasicAuth

req_kw = {
'verify': 'mypem',
'auth': HTTPBasicAuth('u', 'p')
}

cursor = presto.connect(
host='host',
port=port,
protocol='https',
username='u',
requests_kwargs=req_kw,
).cursor()

query = '''select * from x.y limit 1'''
cursor.execute(query)
print cursor.fetchall()
#result is
[(u'2010-02-18 03:00:00.000', u'2010-02-18 00:00:00.000', 3, u'-0.191912651062011660', u'hey', u'there')]

Answer 1

您从 sql 查询中获得的输出来自该格式的数据库。

你有两个选择

自己映射数据（编写自己的 ORM）
学习使用 ORM

选项 1

请注意，我刚刚在此处硬编码了您的查询结果以供测试。

from sqlalchemy.engine import create_engine
from datetime import datetime
from decimal import Decimal

# 2010-02-18 03:00:00.000
dateTimeFormat = "%Y-%m-%d %H:%M:%S.%f"

class hivexy:
    def __init__(self, for_dt, for_d, for_h, value, metric, lat_lon):
        self.for_dt = for_dt
        self.for_d = for_d
        self.for_h = for_h
        self.value = value
        self.metric = metric
        self.lat_lon = lat_lon

    # Pretty Printing on print(hivexy)
    def __str__(self):
        baseString =  ("for_dt: {}\n"
                       "for_d: {}\n"
                       "for_h: {}\n"
                       "value: {}\n"
                       "metric: {}\n"
                       "lat_lon: {}\n")
        return baseString.format(for_dt, for_d, for_h, value, metric, lat_lon)

#engine = create_engine('presto://u:p@host:port',connect_args={'protocol': 'https', 'requests_kwargs': {'verify': 'mypem'}})
#results = engine.execute("select * from 'hive.x.y' limit 1")
results = [(u'2010-02-18 03:00:00.000', u'2010-02-18 00:00:00.000', 3, u'-0.191912651062011660', u'hey', u'there')]

hiveObjects = []

for row in results:
    for_dt = datetime.strptime(row[0], dateTimeFormat)
    for_d = datetime.strptime(row[1], dateTimeFormat)
    for_h = row[2]
    value = Decimal(row[3])
    metric = row[4]
    lat_lon = row[5]

    hiveObjects.append(hivexy(for_dt, for_d, for_h, value, metric, lat_lon))

for hiveObject in hiveObjects:
    print(hiveObject)

选项 2 这使用反射 - 它查询数据库元数据的字段类型，因此您不必在选项 1 中执行所有这些操作。

from sqlalchemy import *
from sqlalchemy.engine import create_engine
from sqlalchemy.schema import *

engine = create_engine('presto://u:p@host:port',connect_args={'protocol': 'https', 'requests_kwargs': {'verify': 'mypem'}})

# Reflection - SQLAlchemy will get metadata from database including field types
hiveXYTable = Table('hive.x.y', MetaData(bind=engine), autoload=True)
s = select([hiveXYTable]).limit(1)
results = engine.execute(s)

for row in results:
    print(row)

python - presto - 时间戳和 decimal(38,18) 作为字符串返回？

python - presto - timestamps and decimal(38,18) returned as strings?

hive

sqlalchemy

presto

pyhive

急速 jdbc:

结果是