import unittest
import psycopg2
import pandas as pd
import re

class TestPostgresQuery(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 setUp(self):
        # Restore all tables to known state before each test
        # This assumes the tables are prepopulated with initial data for testing
        # Restore assignments first because of FKs
        self.cursor.execute("DELETE FROM assignments;")
        # Restore projects (to remove dependency on departments)
        self.cursor.execute("DELETE FROM projects;")
        # Restore employees
        self.cursor.execute("DELETE FROM employees;")
        self.cursor.execute("INSERT INTO employees (employee_id, name, manager_id) VALUES (1, 'Alice Johnson', NULL), (2, 'Bob Smith', 1), (3, 'Carol White', 1), (4, 'David Brown', 2), (5, 'Eve Black', 2), (6, 'Frank Green', 3), (7, 'Grace Lee', 3), (8, 'Hannah Adams', 1);")
        # Restore departments
        self.cursor.execute("DELETE FROM departments;")
        self.cursor.execute("INSERT INTO departments (department_id, department_name) VALUES (1, 'Engineering'), (2, 'HR'), (3, 'Finance'), (4, 'Marketing');")
        # Restore projects
        self.cursor.execute("INSERT INTO projects (project_id, project_name, department_id) VALUES (1, 'Website Redesign', 1), (2, 'Recruitment Drive', 2), (3, 'Budget Planning', 3), (4, 'Product Launch', 4);")
        # Restore assignments
        self.cursor.execute("INSERT INTO assignments (assignment_id, employee_id, project_id) VALUES (1, 2, 1), (2, 4, 1), (3, 5, 4), (4, 2, 4), (5, 3, 2), (6, 6, 2), (7, 7, 2), (8, 8, 3);")
        self.connection.commit()

    def test_all_assignments_present(self):
        """Check if all assignments are present with correct joins."""
        with open("query.sql", "r") as file:
            query = file.read()
        # Reference solution query
        solution_query = '''
        SELECT assignments.assignment_id, employees.name AS employee_name, projects.project_name, departments.department_name
        FROM assignments
        JOIN employees ON assignments.employee_id = employees.employee_id
        JOIN projects ON assignments.project_id = projects.project_id
        JOIN departments ON projects.department_id = departments.department_id
        '''
        self.cursor.execute(solution_query)
        solution_rows = self.cursor.fetchall()
        solution_columns = [desc[0] for desc in self.cursor.description]
        solution_df = pd.DataFrame(solution_rows, columns=solution_columns)
        
        self.cursor.execute(query)
        user_rows = self.cursor.fetchall()
        user_columns = [desc[0] for desc in self.cursor.description]
        user_df = pd.DataFrame(user_rows, columns=user_columns)

        # Normalize columns for comparison
        solution_df = solution_df.applymap(lambda x: normalize_text(str(x)))
        user_df = user_df.applymap(lambda x: normalize_text(str(x)))

        # Check all expected rows are present
        missing_rows = []
        for _, expected_row in solution_df.iterrows():
            expected_dict = expected_row.to_dict()
            mask = (user_df[list(expected_dict.keys())] == pd.Series(expected_dict)).all(axis=1)
            if not mask.any():
                missing_rows.append(expected_dict)
        condition = len(missing_rows) == 0
        if not condition:
            failure_msg = f"The following expected rows are missing:\\n" + "\\n".join(str(r) for r in missing_rows)
        else:
            failure_msg = ""
        _dynamic_test(
            self,
            condition,
            "All expected assignment rows are present with correct joins.",
            failure_msg
        )

    def test_output_columns(self):
        """Check output columns are correct and in any order."""
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        user_columns = set([normalize_text(desc[0]) for desc in self.cursor.description])
        expected_columns = set([
            "assignment_id",
            "employee_name",
            "project_name",
            "department_name"
        ])
        condition = expected_columns == user_columns
        missing = expected_columns - user_columns
        extra = user_columns - expected_columns
        if not condition:
            failure_msg = f"Output columns mismatch. Missing: {missing}. Extra: {extra}."
        else:
            failure_msg = ""
        _dynamic_test(
            self,
            condition,
            "Output includes assignment_id, employee_name, project_name, department_name.",
            failure_msg
        )

    def test_inner_joins_only(self):
        """Check only assignments with valid links in all tables are returned (inner join behavior)."""
        # Remove all assignments and add one with invalid links, but skip foreign key constraint by disabling triggers
        self.cursor.execute("DELETE FROM assignments;")
        self.connection.commit()
        try:
            self.cursor.execute("ALTER TABLE assignments DISABLE TRIGGER ALL;")
            self.cursor.execute("INSERT INTO assignments (assignment_id, employee_id, project_id) VALUES (99, 100, 200);")
            self.connection.commit()
            with open("query.sql", "r") as file:
                query = file.read()
            self.cursor.execute(query)
            rows = self.cursor.fetchall()
            condition = len(rows) == 0
            _dynamic_test(
                self,
                condition,
                "Query returns only assignments with valid links in all tables.",
                "Query returns assignments with missing links; should only return valid ones."
            )
        finally:
            self.cursor.execute("DELETE FROM assignments WHERE assignment_id = 99;")
            self.cursor.execute("ALTER TABLE assignments ENABLE TRIGGER ALL;")
            self.connection.commit()
        # Restore assignments for other tests
        self.cursor.execute("DELETE FROM assignments;")
        self.cursor.execute("INSERT INTO assignments (assignment_id, employee_id, project_id) VALUES (1, 2, 1), (2, 4, 1), (3, 5, 4), (4, 2, 4), (5, 3, 2), (6, 6, 2), (7, 7, 2), (8, 8, 3);")
        self.connection.commit()

    def test_joins_on_correct_columns(self):
        """Check joins use correct columns by removing a join and expecting empty output."""
        # Remove all assignments first (because of FK), then all employees
        self.cursor.execute("DELETE FROM assignments;")
        self.cursor.execute("DELETE FROM employees;")
        self.connection.commit()
        with open("query.sql", "r") as file:
            query = file.read()
        self.cursor.execute(query)
        rows = self.cursor.fetchall()
        condition = len(rows) == 0
        _dynamic_test(
            self,
            condition,
            "Joins are performed on correct columns (employees missing, so output empty).",
            "Query does not join on correct columns: should return no rows if employees table is empty."
        )
        # Restore employees and assignments for other tests
        self.cursor.execute("DELETE FROM employees;")
        self.cursor.execute("INSERT INTO employees (employee_id, name, manager_id) VALUES (1, 'Alice Johnson', NULL), (2, 'Bob Smith', 1), (3, 'Carol White', 1), (4, 'David Brown', 2), (5, 'Eve Black', 2), (6, 'Frank Green', 3), (7, 'Grace Lee', 3), (8, 'Hannah Adams', 1);")
        self.cursor.execute("DELETE FROM assignments;")
        self.cursor.execute("INSERT INTO assignments (assignment_id, employee_id, project_id) VALUES (1, 2, 1), (2, 4, 1), (3, 5, 4), (4, 2, 4), (5, 3, 2), (6, 6, 2), (7, 7, 2), (8, 8, 3);")
        self.connection.commit()

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

Master the art of SQL joins with engaging, real-world examples and hands-on challenges. This course takes you from foundational join concepts to advanced multi-table queries, ensuring you can confidently analyze and combine data from multiple sources.

Explore the essential SQL join types—INNER, LEFT, RIGHT, and FULL OUTER JOIN—through practical scenarios and hands-on challenges.

Level up your SQL skills by mastering multi-table joins, self-joins, and advanced join conditions for complex data analysis.

Master the nuances of NULL handling in joins, optimize join performance, and tackle real-world data analysis challenges.

Challenge: Complex Assignment Matching

Solution

Challenge: Complex Assignment Matching

Solution