Summary  
Demonstrates using the BETWEEN operator in SQL to filter query results within an inclusive range.

General domain of usage  
Database querying

値の範囲を確認するには、`BETWEEN` 演算子を使用します。この演算子には、範囲の **開始値** と **終了値** の2つの値が必要です。また、`AND` キーワードはこれらの値の**間**に配置します。

`BETWEEN` 演算子の構文は次のとおりです:

```sql
SELECT columns 
FROM table 
WHERE column BETWEEN value_from AND value_to;
```

例を見てみましょう:

SELECT name, population
FROM country
WHERE population BETWEEN 100000 AND 3000000;

import unittest
import psycopg2
import pandas as pd

class TestTask(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        cls.connection = psycopg2.connect(
            host="localhost",
            user="agent",
            password="qwerty",
            dbname="testdb",
            sslmode="disable"
        )
        cls.cursor = cls.connection.cursor()

    def test_correct_columns_selected(self):
        """Check that only name, capital, and population columns are selected and in correct order."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        columns = [desc[0] for desc in self.cursor.description]
        expected_columns = ["name", "capital", "population"]
        _dynamic_test(
            self,
            columns == expected_columns,
            "Correct columns are selected in the correct order.",
            f"Columns selected are {columns}, expected {expected_columns}."
        )

    def test_between_operator_and_values(self):
        """Check that the query uses BETWEEN with correct values (6000000 and 80000000)."""
        with open("query.sql", "r") as file:
            query = file.read().lower().replace("\\n", " ")
        has_between = "between" in query
        has_6000000 = "6000000" in query
        has_80000000 = "80000000" in query
        condition = has_between and has_6000000 and has_80000000
        _dynamic_test(
            self,
            condition,
            "BETWEEN operator with correct values is used.",
            "Query must use BETWEEN operator with 6000000 and 80000000."
        )

    def test_order_by_capital_ascending(self):
        """Check that the result is ordered by capital ascending."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        if not rows:
            _dynamic_test(
                self,
                False,
                "Result is ordered by capital ascending.",
                "Query result is empty, cannot check ordering."
            )
            return
        capitals = [row[1] for row in rows]
        sorted_capitals = sorted([c for c in capitals if c is not None])
        # Place None at the end if present
        if any(c is None for c in capitals):
            sorted_capitals += [None] * capitals.count(None)
        condition = capitals == sorted_capitals
        _dynamic_test(
            self,
            condition,
            "Result is ordered by capital ascending.",
            f"Result is not ordered by capital ascending: {capitals}"
        )

    def test_correct_rows_selected(self):
        """Check that only countries with population between 6000000 and 80000000 are returned."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        # The population column is at index 2
        for row in rows:
            population = row[2]
            condition = population is not None and 6000000 <= population <= 80000000
            if not condition:
                _dynamic_test(
                    self,
                    False,
                    "All rows have population between 6000000 and 80000000.",
                    f"Row with population {population} is not in the required range."
                )
                return
        _dynamic_test(
            self,
            True,
            "All rows have population between 6000000 and 80000000.",
            "Some rows have population outside the required range."
        )

    def test_query_syntax(self):
        """Check that the query executes without syntax errors."""
        with open("query.sql", "r") as file:
            query = file.read()
        try:
            self.cursor.execute(query)
            _dynamic_test(
                self,
                True,
                "Query executes without syntax errors.",
                "Query has a syntax error."
            )
        except Exception as e:
            _dynamic_test(
                self,
                False,
                "Query executes without syntax errors.",
                f"Query has a syntax error: {e}"
            )

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

def normalize_text(text):
    text = text.lower()
    text = re.sub(r"\s{2,}", " ", text)
    text = re.sub(r"\s*([,:?])\s*", r"\1 ", text)
    return text.strip()

if __name__ == "__main__":
    unittest.main()


test_solution.py

このモジュールは、SQLの世界を探求したい初心者に最適です。データベース管理を始めたばかりの方や、アプリケーション開発プロジェクトでSQLを活用したい方にも対応しています。本コースでは、SQLの基本を網羅しています。データのクエリや管理から、実際のアプリケーションへのシームレスな統合まで、SQLの可能性を最大限に活用する方法を迅速に学ぶことができます。

このコースは、SQLの世界を探求したい初心者に最適です。データベース管理を始めたばかりの方や、アプリケーション開発プロジェクトでSQLを活用したい方にも対応しています。本コースでは、SQLの基本から応用までを網羅しており、データのクエリや管理、実際のアプリケーションへの統合方法までを迅速に習得できます。コース修了時には、SQLを用いて実践的な課題を解決し、開発プロセスを向上させる自信とスキルが身につきます。

値の範囲を確認する

解答