[Solved] Linq join query returning less records than Sql Query in ASP.Net Core MVC

I am working in Asp.Net Core MVC project with MYSQL database.

Issue: LINQ query does not return the correct number of rows compared to MYSQL query. 

Repository Class Code:

public IEnumerable<MappingCost> GetAllMappingCost()
{
    return context.MappingCost;
}

public IEnumerable<HdrPearlProject> GetProjectDDL()
{
    return context.HdrPearlProject;
}

public IEnumerable<HdrFdpScenarios> GetScenarioDDL()
{
    return context.HdrFdpScenarios;
}

Controller LINQ Query:

             var data = (from mc in _repository.GetAllMappingCost().ToList()
			join pp in _repository.GetProjectDDL().ToList() on new { mc.ProjectId } equals new { pp.ProjectId }
			join hfs in _repository.GetScenarioDDL().ToList() on new { mc.StudyId, mc.ScenarioId } equals new { hfs.StudyId, hfs.ScenarioId }
			select new
			{
				mc.MappingCapexId,
				mc.MappingId,
				hfs.StudyId,
				hfs.StudyName,
				hfs.ScenarioId,
				hfs.CombinedName,
				mc.FdpCategory,
				mc.FdpProduct,
				mc.Allocation,
				pp.ProjectId,
				pp.ProjectName,
				mc.PearlCosttype,
				mc.Parent1,
				mc.Parent2,
				mc.Parent3,
				mc.Item
			}).ToList();

Above Linq query returns a total of 18 rows

Whereas, on running below query in MYSQL workbench, I get total of 81 rows.

SELECT *
FROM mapping_cost mc, hdr_fdp_scenarios hsc, hdr_pearl_project hpp
WHERE mc.study_id = hsc.study_id and mc.scenario_id = hsc.scenario_id AND mc.project_id = hpp.project_id;

OR

SELECT *
FROM mapping_cost mc
inner join hdr_fdp_scenarios hsc on mc.study_id = hsc.study_id
inner join hdr_pearl_project hpp on mc.scenario_id = hsc.scenario_id AND mc.project_id = hpp.project_id;

NOTE:

1. Mappingcost table has total of 121 rows (in which some "study_id" and "scenario_id" column data is null) ---- Controller screen table

2. HdrPearlProject table has total of 41 rows ---- master/parent table

3. HdrFdpScenarios table has total of 125 rows ---- master/parent table.

I am first time facing this issue and after checking several times, I don't understand why the LINQ count doesn't match with MYSQL query count.

Please let me know what is wrong in my LINQ query.

Thank you in advance.