hacker_rank_aggregation_challenges.ipynb

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    "# hacker rank MYSQL aggregation challenges.\n",
    "\n",
    "### count function\n",
    "1.\n",
    "```mysql\n",
    "SELECT COUNT(*) FROM CITY\n",
    "WHERE POPULATION > 100000\n",
    "```\n",
    "### sum function\n",
    "2.\n",
    "```mysql\n",
    "SELECT SUM(POPULATION) FROM CITY\n",
    "WHERE DISTRICT = 'CALIFORNIA'\n",
    "```\n",
    "### averages\n",
    "3.\n",
    "```mysql\n",
    "SELECT AVG(POPULATION) FROM CITY\n",
    "WHERE DISTRICT = 'CALIFORNIA'\n",
    "```\n",
    "### population averages\n",
    "4.\n",
    "```mysql\n",
    "SELECT ROUND(AVG(POPULATION)) FROM CITY\n",
    "```\n",
    "### japan population\n",
    "5.\n",
    "```mysql\n",
    "SELECT SUM(POPULATION) FROM CITY\n",
    "WHERE COUNTRYCODE = 'JPN'\n",
    "```\n",
    "### population density difference\n",
    "6.\n",
    "```mysql\n",
    "SELECT MAX(POPULATION) - MIN(POPULATION) FROM CITY\n",
    "```"
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