This topic describes the usage and limits of Java user-defined table functions (UDTFs) and Python UDTFs.

Usage

The following statements provide examples to show typical use cases of UDTFs in MaxCompute 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;

For more information about UDTFs, see Java UDF and Python 2 UDFs.

Limits

When you use UDTFs, take note of the following limits:
  • A SELECT clause cannot contain 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;