SQLAlchemy: How to make an integer column auto_increment (and unique) without making it a primary key?

Question

I am using Flask extension for SQLAlchemy to define my database model. I want an id column to be int type and with auto_increment property but without making it a primary key. How do I achieve it?

I tried this:

from flask import Flask, jsonify
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:ajay@localhost/pydb'
app.config['SQLALCHEMY_ECHO'] = True
db = SQLAlchemy(app)

class Scenario(db.Model):
    scid = db.Column(db.Integer, nullable=False, unique=True, autoincrement=True)
    scenario_name = db.Column(db.String(100), primary_key=True)
    scenario_description = db.Column(db.String(200), nullable=False)
    image_id = db.Column(db.Integer, db.ForeignKey('images.id', onupdate='CASCADE', ondelete='CASCADE'))

    def __init__(self, scenario_name, scenario_description, image_id=None):
        self.scenario_name = scenario_name
        self.scenario_description = scenario_description
        self.image_id = image_id

    def __repr__(self):
        return '<Scenario %r, %r, %r>' % (self.scenario_name, self.scenario_description, self.image_id)

but this doesn't set the scid column as auto_increment.

Solution

You can add an AUTO_INCREMENT not primary key but you can't have two AUTO_INCREMENT fields

If you don't have AUTO_INCREMENT you can add an AUTO_INCREMENT and UNIQUE whith something like this:

ALTER TABLE `items` ADD `AutoInc` INT NOT NULL AUTO_INCREMENT, ADD UNIQUE (`AutoInc`)