I have 3 tables `Employee`,`Project` and `Assignment`. An employee can be assigned to multiple projects and one project can have multiple employees. `Assignment` table keeps many to many relationship between employees and projects. I want a sql query in sql server that returns a list of employees that have ever worked on more than one project at the same time.

Staructure of tables

**Table Employee**

```
EmpId,
EmpName

```

**Table Project**

```
ProjId,ProjName,ProjStartDate,ProjEndDate

```

**Assignment**

```
AssignmentId,ProjId,EmpId,AssStartDate,AssEndDate

```