"""add email column to users
Revision ID: abc123
"""
from alembic import op
import sqlalchemy as sa
def upgrade():
    op.add_column('users', sa.Column('email', sa.String(255), nullable=True))
    op.create_index('ix_users_email', 'users', ['email'], unique=True)
def downgrade():
    op.drop_index('ix_users_email')
    op.drop_column('users', 'email')

-- V2__add_email_to_users.sql
ALTER TABLE users ADD COLUMN email VARCHAR(255);
CREATE UNIQUE INDEX ix_users_email ON users(email);
 
-- 回滚脚本 (单独文件 U2__rollback_add_email.sql)
-- 逆向操作

// schema.prisma 变更
model User {
  id    Int     @id @default(autoincrement())
  name  String
  email String? @unique  // 新增字段
}

# 默认仅生成迁移，不执行数据库变更
npx prisma migrate dev --name add-email-to-users --create-only

# 开发环境应用迁移
npx prisma migrate dev
 
# 生产环境应用已审核并提交的迁移
npx prisma migrate deploy

# users/migrations/0002_add_email.py
from django.db import migrations, models
class Migration(migrations.Migration):
    dependencies = [('users', '0001_initial')]
    operations = [
        migrations.AddField(
            model_name='user',
            name='email',
            field=models.EmailField(unique=True, null=True),
        ),
    ]

# db/migrate/20260617_add_email_to_users.rb
class AddEmailToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :email, :string
    add_index :users, :email, unique: true
  end
end

rails db:migrate         # 执行迁移
rails db:rollback        # 回滚上一次
rails db:rollback STEP=3 # 回滚最近 3 次