add Universal Sets

Author: dimitri-yatsenko

book/50-queries/005-fetch.ipynb

@@ -4,7 +4,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# `fetch`\n",
+    "#  Fetch\n",
+    "\n",
+    "(AI-generated template. Work in progress.)\n",
     "\n",
     "The `fetch` and `fetch1` commands in DataJoint are essential tools for retrieving data from tables. These commands allow users to query data in a structured and efficient manner, supporting both single-row and multi-row results. Understanding their usage is critical for navigating and utilizing your DataJoint pipeline effectively.\n",
     "\n",

book/50-queries/060-universal.ipynb

@@ -0,0 +1,25 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Universal Sets\n",
+    "\n",
+    "Several types of queries require an additional construct, which we describe as the *Universal Set*, which is constructed using the `dj.U` class."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": []
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}