Major Description
Let's assume that we have a udf called splitUDF which outputs a map data.
The SQL
select
g['a'], g['b']
from
( select splitUDF(x) as g from table) tbl
will be optimized to the same logical plan of
select splitUDF(x)['a'], splitUDF(x)['b'] from table
which means that the splitUDF is executed twice instead of once.
The optimization is from CollapseProject.
I'm not sure whether this is a bug or not. Please tell me if I was wrong about this.