如何从psycopg2游标获取列名列表？

Question

我想要一种直接从所选列名生成列标签的一般方法,并回想一下,看到python的psycopg2模块支持此功能.

Answer 1

来自Mark Lutz的"Programming Python":

curs.execute("Select * FROM people LIMIT 0")
colnames = [desc[0] for desc in curs.description]

Answer 2

您可以做的另一件事是创建一个游标,您可以通过它们的名称引用您的列(这是首先引导我访问此页面的需要):

import psycopg2
from psycopg2.extras import RealDictCursor

ps_conn = psycopg2.connect(...)
ps_cursor = psql_conn.cursor(cursor_factory=RealDictCursor)

ps_cursor.execute('select 1 as col_a, 2 as col_b')
my_record = ps_cursor.fetchone()
print (my_record['col_a'],my_record['col_b'])

>> 1, 2

Answer 3

要在单独的查询中获取列名,可以查询information_schema.columns表.

#!/usr/bin/env python3

import psycopg2

if __name__ == '__main__':
  DSN = 'host=YOUR_DATABASE_HOST port=YOUR_DATABASE_PORT dbname=YOUR_DATABASE_NAME user=YOUR_DATABASE_USER'

  column_names = []

  with psycopg2.connect(DSN) as connection:
      with connection.cursor() as cursor:
          cursor.execute("select column_name from information_schema.columns where table_schema = 'YOUR_SCHEMA_NAME' and table_name='YOUR_TABLE_NAME'")
          column_names = [row[0] for row in cursor]

  print("Column names: {}\n".format(column_names))

要在与数据行相同的查询中获取列名,可以使用游标的description字段:

#!/usr/bin/env python3

import psycopg2

if __name__ == '__main__':
  DSN = 'host=YOUR_DATABASE_HOST port=YOUR_DATABASE_PORT dbname=YOUR_DATABASE_NAME user=YOUR_DATABASE_USER'

  column_names = []
  data_rows = []

  with psycopg2.connect(DSN) as connection:
    with connection.cursor() as cursor:
      cursor.execute("select field1, field2, fieldn from table1")
      column_names = [desc[0] for desc in cursor.description]
      for row in cursor:
        data_rows.append(row)

  print("Column names: {}\n".format(column_names))

Answer 4

如果您希望获得已关联列标题的 Pandas 数据框，请尝试以下操作：

import psycopg2, pandas

con=psycopg2.connect(
    dbname=DBNAME, 
    host=HOST, 
    port=PORT, 
    user=USER, 
    password=PASSWORD
)

sql = """
select * from x
"""

d = pandas.read_sql_query(sql,con)

con.close()

print(type(d))

print(pandas.DataFrame.head(d))

Answer 5

如果你想从db查询中获得一个命名的元组obj,你可以使用以下代码片段:

from collections import namedtuple

def create_record(obj, fields):
    ''' given obj from db returns named tuple with fields mapped to values '''
    Record = namedtuple("Record", fields)
    mappings = dict(zip(fields, obj))
    return Record(**mappings)

cur.execute("Select * FROM people")
colnames = [desc[0] for desc in cur.description]
rows = cur.fetchall()
cur.close()
result = []
for row in rows:
    result.append(create_record(row, colnames))

这允许您访问记录值,就好像它们是类属性,即

record.id,record.other_table_column_name等

甚至更短

from psycopg2.extras import NamedTupleCursor
with cursor(cursor_factory=NamedTupleCursor) as cur:
   cur.execute("Select * ...")
   return cur.fetchall()

Answer 6

执行 SQL 查询后，按照 2.7 中编写的 python 脚本编写

total_fields = len(cursor.description)    
fields_names = [i[0] for i in cursor.description   
    Print fields_names