10_sql/JOIN_basic.exercises.ipynb

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   "source": [
    "# SQL joining (merging) tables (exercises)"
   ]
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   "source": [
    "## Preparation"
   ]
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    "For this section you need `chinook.db` database file and working `%sql` magic.  \n",
    "If you don't have it, please go back to the [previous section](../09_sql/connect_to_database.ipynb) and follow the instructions.  \n",
    "The following code should not produce any errors:"
   ]
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   "source": [
    "%load_ext sql\n",
    "%sql sqlite:///chinook.db"
   ]
  },
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   "source": [
    "## Exercise: Customer invoices"
   ]
  },
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   "source": [
    "Use `LEFT JOIN` of tables `customers` and `invoice` to build a table listing all invoices per a customer.  \n",
    "The table should have these columns:\n",
    "- `CustomerId`\n",
    "- `FirstName`\n",
    "- `LastName`\n",
    "- `InvoiceId`\n",
    "\n",
    "What would be the primary key for this table?"
   ]
  },
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   "source": [
    "## Exercise: Customers without invoices?"
   ]
  },
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   "source": [
    "Would customers without any invoice be visible in the result table produced above?\n",
    "\n",
    "Check whether such customers exist there."
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Exercise: Double join"
   ]
  },
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   "source": [
    "*In short:* For each customer we want to know totals: how many tracks were bought and for what total price.\n",
    "\n",
    "Build a temporary table `customer_summary` with the following columns:\n",
    "The table should have these columns:\n",
    "- `CustomerId` based on `customers`.\n",
    "- `TotalTracksNum` - total number of tracks bought by the customer.\n",
    "- `TotalPrice` - total sum of prices payed by the customer.\n",
    "\n",
    "Use tables `customers`, `invoice` and `invoice_items`."
   ]
  }
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