创建索引

练习内容

-- 创建单列索引\nCREATE INDEX idx_users_email ON users(email);\n\n-- 创建复合索引\nCREATE INDEX idx_orders_user_status ON orders(user_id, status);\n\n-- 创建唯一索引\nCREATE UNIQUE INDEX idx_users_email_unique ON users