Advance multiple join query table

Hi i have relations database design like this design database relationship at

How can i find the names of all employees who are working on projects for ‘Client A’, including the names of those projects and the tasks associated with them.

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Bobby Iliev
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May 6, 2024


I believe that the following should work for you:

    Departments ON Employees.DepartmentID = Departments.DepartmentID
    Projects ON Departments.DepartmentID = Projects.DepartmentID
    Clients ON Projects.ProjectID = Clients.ProjectID
    Tasks ON Projects.ProjectID = Tasks.ProjectID
    Clients.ClientName = 'Client A';

If you need additional adjustments or modifications to the query, please feel free to ask!

For anyone interested in learning more about SQL in general, I could suggest this free eBook:

💡 Introduction to SQL eBook



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May 5, 2024

Heya @diko23,

To solve the problem of finding the names of all employees working on projects for “Client A”, including the names of those projects and the tasks associated with them, you will need to perform multiple joins across your tables. Since there’s no direct relation between employees and clients, you will join through the Projects and Departments tables.

Here’s how you can construct this query in SQL, assuming you’re using MySQL or PostgreSQL, which both follow similar SQL syntax for this kind of operation:

    Clients c
    Projects p ON c.ProjectID = p.ProjectID
    Tasks t ON p.ProjectID = t.ProjectID
    Departments d ON p.DepartmentID = d.DepartmentID
    Employes e ON d.DepartmentID = e.DepartmentID
    c.ClientName = 'Client A';

Explanation of the SQL Query:

  1. FROM Clients c: Start from the Clients table, which contains information about which client is associated with which project.

  2. JOIN Projects p ON c.ProjectID = p.ProjectID: Join the Clients table to the Projects table to get details about the projects that belong to the client.

  3. JOIN Tasks t ON p.ProjectID = t.ProjectID: Join the Projects table to the Tasks table to get information about the tasks associated with each project.

  4. JOIN Departments d ON p.DepartmentID = d.DepartmentID: Since employees are linked to projects via departments, join the Projects table to the Departments table.

  5. JOIN Employes e ON d.DepartmentID = e.DepartmentID: Finally, join the Departments table to the Employees table to list all employees who are in the department related to the project.

  6. WHERE c.ClientName = ‘Client A’: Filter the results to include only those entries that are related to ‘Client A’.

This query will give you the names of the employees (EmployeName), the names of the projects (ProjectName), and descriptions of the tasks (TaskDescription) that are associated with “Client A”.

Additional Notes:

  • Make sure that all column names match exactly what’s in your database, as SQL is case-sensitive in some setups.
  • This query assumes that every project is assigned to exactly one department, and departments are not shared between different projects. If the business logic differs (e.g., projects can span multiple departments), the SQL might need adjusting.
  • The query also assumes that all projects for a client will have tasks and that there are employees in every department.

This approach gives a comprehensive look at the teams working for “Client A” from a project and task perspective. If you have any more specific requirements or encounter any issues, feel free to provide more details!

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