Count the maximum number of clients and their manager ID using three tables
You cannot name a column in mysql with a statement like MostClient = count(*)
Use the AS keyword count(*) AS MostClient.
I think the next problem you are going to encounter is the other columns that are not aggregates are missing from your group by.
Also, I don't see how the count(*) is going to equal the b.buildingid.
Best of luck!