litvol

import re

keywords = r"(SELECT|WHERE|FROM|AND|OR|NOT)"
patterns = [
	(keywords, lambda scanner, token: {"token_type": "keyword", "token": token}),
	(r"[a-zA-Z_][a-zA-Z_0-9]*", lambda s, t: {"token_type": "name", "token": t}),
	(r"\*", lambda s, t: {"token_type": "all_cols","token":  t}),
	(r">=|>|<=|<|=", lambda s, t: {"token_type": "operator","token":  t}),
	(r"[-+]?\d*\.\d+", lambda s, t: {"token_type": "float","token":  t}),
	(r"\d+", lambda s, t: {"token_type": "integer","token":  t}),

litvol

class Parser(self):
	def advance(self):
			""" Advance the tokens in use
			"""
			self.current_token, self.next_token = self.next_token, next(self.tokens, None)


	def accept(self, expected, raise_err = True):
		""" Helper function to check if the next token is what we expect

litvol

def nested_loop_join(left: List[dict], right: List[dict], on: str, how: str) -> List[dict]:
	""" Nested loop JOIN strategy: For every row in outer, find matching one in inner

		If left/right JOIN and there's no match on inner, return outer. Else, skip

		Params:
			left (list<dict>) - List of dicts representing one relation
			right (list<dict>) - List of dicts representing the other relation
			on (string) - The key in the relations to JOIN on
			how (string) - The JOIN (left, right, inner) 

litvol

version: '3.1'

services:
  database:
    image: "postgres"
    restart: "always"
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
      - POSTGRES_DB=db

litvol

SELECT 
	STUFF
	(
		(
					  SELECT '-> ' + physical_name AS 'data()' 
					  FROM sys.database_files dbfiles
					  WHERE fg.data_space_id = dbfiles.data_space_id
					  FOR XML PATH(''), TYPE
		).value('.', 'VARCHAR(MAX)'), 1, 2, '' 
	) as files_partition_could_be_in,

litvol

import pandas as pd
stock = pd.read_csv('/datasets/stock_upd.csv')

stock['item_lowercase'] = stock['item'].str.lower()

apple = stock[stock['item_lowercase'].str.contains('apple')]['count'].sum()
samsung = stock[stock['item_lowercase'].str.contains('samsung')]['count'].sum()

stock['item_lowercase'] = stock['item_lowercase'].drop_duplicates()
stock = stock.dropna().reset_index(drop=True)

litvol

Postgres Intro Exercises

Простые запросы

Задача #1

Кто летел позавчера рейсом Москва (SVO) — Новосибирск (OVB) на месте 1A, и когда он забронировал свой билет?

select t.passenger_name,

litvol

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Графовые базы данных Neo4j

По материалам:

• Основы работы с Neo4j в браузере
Введение в язык запросов