3-joins.ipynb

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   "source": [
    "> The slides and course material are copyrighted, and licensed under the [GNU General Public License](LICENSE)."
   ]
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   "source": [
    "-----\n",
    "\n",
    "Run this section to set up your database. If you need to reset the database, you can click the Restart button."
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "%pip install -qq jupysql sqlalchemy"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "from sqlalchemy import create_engine\n",
    "from create_database import create_database\n",
    "\n",
    "engine = create_engine('sqlite:///:memory:')\n",
    "create_database(engine)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
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   "source": [
    "%reload_ext sql\n",
    "%config SqlMagic.displaycon = False\n",
    "%config SqlMagic.feedback = 0\n",
    "%sql engine"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "-----"
   ]
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   "source": [
    "# 3. Joins\n",
    "\n",
    "In this section, we will learn how to join data from more than one table in a database.\n",
    "\n",
    "Joins allow you to pull together meaningful information scattered across different tables in a database.\n",
    "\n",
    "- Combine data from multiple tables based on a related column\n",
    "- Fetch comprehensive data using logical relationships\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Inner Join\n",
    "\n",
    "- An inner join matches table rows based on some condition\n",
    "- Specifies conditions which pairs of rows satisfy"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Find students who scored more than 60 in tests."
   ]
  },
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   "source": [
    "%%sql\n",
    "\n",
    "SELECT \n",
    "  FirstName, \n",
    "  LastName, \n",
    "  Code AS Course,\n",
    "  Grade\n",
    "FROM \n",
    "  Students \n",
    "  INNER JOIN Grades \n",
    "    ON Students.SID = Grades.SID\n",
    "WHERE\n",
    "  Grade > 60"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Outer Join\n",
    "\n",
    "- An outer join matches table rows based on some condition\n",
    "- Some rows have no match, and are \"lost\", or \"dangle\"\n",
    "- Outer joins include dangles in the results and use NULLs to fill in the blanks"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "List all students and their grades, but also include students who don't have any grades recorded yet."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "%%sql\n",
    "\n",
    "SELECT \n",
    "  FirstName, \n",
    "  LastName, \n",
    "  Code AS Course,\n",
    "  Grade\n",
    "FROM \n",
    "  Students \n",
    "  LEFT OUTER JOIN Grades \n",
    "    ON Students.SID = Grades.SID"
   ]
  }
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