{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Create A View\n",
    "\n",
    "We can store a query in the database as a view.\n",
    "\n",
    "Let's imagine that we often need the record set that gives maximum and minimum pressure by country.\n",
    "\n",
    "Here's the SQL from the previous chapter that generated it:\n",
    "\n",
    "```sql\n",
    "SELECT\n",
    "    f.country_code,\n",
    "    MAX(r.temp) AS max_temp,\n",
    "    MIN(r.temp) AS min_temp\n",
    "FROM readings AS r JOIN flights AS f\n",
    "    ON r.flight = f.name\n",
    "GROUP BY f.country_code\n",
    "```\n",
    "\n",
    "Let's use this to create view. First we connect to our database:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<sqlalchemy.engine.result.ResultProxy at 0x10d0926a0>"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import sqlalchemy as sa\n",
    "import pandas as pd\n",
    "engine = sa.create_engine('sqlite:///flight.db')\n",
    "connection = engine.connect()\n",
    "connection.execute(\"PRAGMA foreign_keys=on\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "And then, with one extra clause, we create our view:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<sqlalchemy.engine.result.ResultProxy at 0x10d08da58>"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sql = \"\"\"\n",
    "    CREATE VIEW max_min_temp_by_country AS\n",
    "    SELECT\n",
    "        f.country_code,\n",
    "        MAX(r.temp) AS max_temp,\n",
    "        MIN(r.temp) AS min_temp\n",
    "    FROM readings AS r JOIN flights AS f\n",
    "        ON r.flight = f.name\n",
    "    GROUP BY f.country_code\n",
    "\"\"\"\n",
    "connection.execute(sql)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can include the view in a SELECT statement in exactly the same way as a table:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>country_code</th>\n",
       "      <th>max_temp</th>\n",
       "      <th>min_temp</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>GB</td>\n",
       "      <td>26.9</td>\n",
       "      <td>23</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "  country_code  max_temp  min_temp\n",
       "0           GB      26.9        23"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sql = \"\"\"\n",
    "    SELECT *\n",
    "    FROM max_min_temp_by_country\n",
    "    WHERE country_code = 'GB'\n",
    "\"\"\"\n",
    "pd.read_sql(sql, connection)"
   ]
  }
 ],
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