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To retrieve data from an already established database using Flask Sqlalchemy, you can follow the following steps:

Import the necessary modules:

from flask import Flask from flask_sqlalchemy import SQLAlchemy

Initialize the Flask app and the Sqlalchemy object:

app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'database_connection_string' db = SQLAlchemy(app)

Define the database model:

class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True, nullable=False) email = db.Column(db.String(120), unique=True, nullable=False) password = db.Column(db.String(80), nullable=False)

Query the database to retrieve the data:

# Retrieve all users users = User.query.all() # Retrieve a specific user by id user = User.query.get(id) # Retrieve a specific user by username user = User.query.filter_by(username='username').first()

Use the retrieved data as needed in your application.

Note: Make sure to replace 'databaseconnectionstring' with the actual connection string for your database.