Conversion of SQL server merge code to equivalent Postgresql code

How to convert merge of SQL server to equivalent postgresql code: I am new to SQL Server and not aware how merge behaves

merge PortfolioAssetClassBenchmark_Subset as t
 using @inputBenchmark as s
    on t.PortfolioId = @PortfolioId and t.StartDate = s.F_STARTDATE
 when matched and isnull(s.F_BENCHMARK, 0) != 0 and t.AssetClassBenchmarkId != s.F_BENCHMARK then
    update set 
    t.AssetClassBenchmarkId = s.F_BENCHMARK
 when matched and isnull(s.F_BENCHMARK, 0) = 0 then
    delete  
 when not matched by target and isnull(s.F_BENCHMARK, 0) != 0 then
    insert (PortfolioId, StartDate, AssetClassBenchmarkId)
    values (@PortfolioId, s.F_STARTDATE, s.F_BENCHMARK) 
 when not matched by source and @clearExisting != 0 then
    delete
 output  inserted.AssetClassBenchmarkId [InsertedAssetClassBenchmarkId]
    , inserted.StartDate [InsertedStartDate]
    , deleted.AssetClassBenchmarkId [DeletedAssetClassBenchmarkId]
    , deleted.StartDate [DeletedStartDate] 
 into @tmp