You are utilizing Google BigQuery as your data warehouse solution. Users have raised concerns about the performance of a particular query which persists in running sluggishly, irrespective of the time of execution. The query in question is:

SELECT country, state, city FROM [myproject:mydataset.mytable] GROUP BY country

Upon examining the query plan within the Read section of Stage:1, you observe certain details that could be indicative of the underlying issue. What is the most probable reason for the delay in the execution of this query?

Exam-Like

Users are running too many concurrent queries in the system

5.8%

The [myproject:mydataset.mytable] table has too many partitions

13.6%

Either the state or the city columns in the [myproject:mydataset.mytable] table have too many NULL values

6.8%

Most rows in the [myproject:mydataset.mytable] table have the same value in the country column, causing data skew

73.8%

Google Professional Data Engineer