UDTF usage

In typical cases, a UDTF is used as follows in Structured Query Language (SQL):

select user_udtf(col0, col1, col2) as (c0, c1) from my_table; 
select user_udtf(col0, col1, col2) as (c0, c1) from (select * from my_table distribute by key sort by key) t;
select reduce_udtf(col0, col1, col2) as (c0, c1) from (select col0, col1, col2 from (select map_udtf(a0, a1, a2, a3) as (col0, col1, col2) from my_table) t1 distribute by col0 sort by col0, col1) t2;

UDTFs are subject to the following limits:

• A select clause cannot contain any other expressions.

  select value, user_udtf(key) as mycol ...

• A UDTF cannot be nested.

  select user_udtf1(user_udtf2(key)) as mycol...

• A select clause cannot be used with a group by, distribute by, or sort by clause.

  select user_udtf(key) as mycol ... group by mycol