python - psycopg2 カーソルから列名のリストを取得するにはどうすればよいですか?

Question

選択した列名から列ラベルを直接生成する一般的な方法が欲しいのですが、python の psycopg2 モジュールがこの機能をサポートしていることを思い出してください。

Answer 1

Mark Lutz 著「Programming Python」より:

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

Answer 2

別のクエリで列名を取得するには、information_schema.columns テーブルにクエリを実行できます。

#!/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))

データ行と同じクエリで列名を取得するには、カーソルの説明フィールドを使用できます。

#!/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 3

cursor.fetchone()列のリストを取得するには、クエリの後に使用する必要があることに気付きましたcursor.description(つまり[desc[0] for desc in curs.description])

Answer 4

#!/usr/bin/python
import psycopg2
#note that we have to import the Psycopg2 extras library!
import psycopg2.extras
import sys

def main():
    conn_string = "host='localhost' dbname='my_database' user='postgres' password='secret'"
    # print the connection string we will use to connect
    print "Connecting to database\n ->%s" % (conn_string)

    # get a connection, if a connect cannot be made an exception will be raised here
    conn = psycopg2.connect(conn_string)

    # conn.cursor will return a cursor object, you can use this query to perform queries
    # note that in this example we pass a cursor_factory argument that will
    # dictionary cursor so COLUMNS will be returned as a dictionary so we
    # can access columns by their name instead of index.
    cursor = conn.cursor(cursor_factory=psycopg2.extras.DictCursor)

    # tell postgres to use more work memory
    work_mem = 2048

    # by passing a tuple as the 2nd argument to the execution function our
    # %s string variable will get replaced with the order of variables in
    # the list. In this case there is only 1 variable.
    # Note that in python you specify a tuple with one item in it by placing
    # a comma after the first variable and surrounding it in parentheses.
    cursor.execute('SET work_mem TO %s', (work_mem,))

    # Then we get the work memory we just set -> we know we only want the
    # first ROW so we call fetchone.
    # then we use bracket access to get the FIRST value.
    # Note that even though we've returned the columns by name we can still
    # access columns by numeric index as well - which is really nice.
    cursor.execute('SHOW work_mem')

    # Call fetchone - which will fetch the first row returned from the
    # database.
    memory = cursor.fetchone()

    # access the column by numeric index:
    # even though we enabled columns by name I'm showing you this to
    # show that you can still access columns by index and iterate over them.
    print "Value: ", memory[0]

    # print the entire row 
    print "Row: ", memory

if __name__ == "__main__":
    main()