引用同一个hdfs表将连接到impala中的50个union all语句中，这会导致内存问题

Select a,case statement
From a inner join b
On a=b

Union all

Select a,case statement
From a inner join b
On a=b

Union all

Select a,case statement
From a inner join b
On a=b

Union all

Select a,case statement
From a inner join b
On a=b