CORRELATED SUBQUERIES

SubQuery : 
Simple subquery doesn't use values from the outer query and is being calculated only once:

SELECT id, first_name FROM student_details
WHERE id IN (SELECT student_id FROM student_subjects

WHERE subject= 'Science');

 
CoRelated Subquery  -
Query To Find all employees whose salary is above average for their department

SELECT employee_number, name FROM employees emp
WHERE salary > ( SELECT AVG(salary) FROM employees

WHERE department = emp.department);

Postgres : Database (docker) 

FastApi : Create Production ready Api

 FastApi : Create Production ready Api (faster than Flask)

https://fastapi.tiangolo.com/

Features

1. Asynchronous

2. High Perfromance

3. Less Code

4. Data Type  and Data Models auto Conversions

5. Auto Documentation

    - swagger (/docs)

    - ReDoc   (/redoc)

Pre-Req:

Install and activate virtual environment to be safe.

Steps:

1. pip install fastapi
2. pip install hypercorn #server
3. touch main.py
4. copy paste below code
5. hypercorn main:app --reload

from fastapi import FastAPI

from pydantic import BaseModel #model

# import requests

app = FastAPI()

db = []

class Person(BaseModel):

name: str

@app.get('/')

def index():return {'person' : 'name'}

@app.get('/persons')

def get_persons():

results = []

for person in db:results.append(person)

return results

@app.get('/persons/{person_id}')

def get_person(person_id: int):return db[person_id-1]

@app.post('/persons')

def create_person(person: Person):

db.append(person)

return db[-1]

@app.delete('/persons/{person_id}')

def delete_person(person_id: int):

db.pop(person_id-1)

return {}