hequn8128 commented on a change in pull request #11531:
[FLINK-16748][python][doc] Add Python UDTF doc
URL: https://github.com/apache/flink/pull/11531#discussion_r407952095
##########
File path: docs/dev/table/functions/udfs.zh.md
##########
@@ -247,53 +255,51 @@ tableEnv.sqlQuery("SELECT a, word, length FROM MyTable
LEFT JOIN LATERAL TABLE(s
</div>
<div data-lang="python" markdown="1">
-{% highlight python %}
-'''
-Java code:
+In order to define a Python table function, one can extend the base class
TableFunction in pyflink.table.udtf and Implement an evaluation method. The
behavior of a Python table function is determined by the evaluation method
which is named eval.
-// The generic type "Tuple2<String, Integer>" determines the schema of the
returned table as (String, Integer).
-// The java class must have a public no-argument constructor and can be
founded in current java classloader.
-public class Split extends TableFunction<Tuple2<String, Integer>> {
- private String separator = " ";
-
- public void eval(String str) {
- for (String s : str.split(separator)) {
- // use collect(...) to emit a row
- collect(new Tuple2<String, Integer>(s, s.length()));
- }
- }
-}
-'''
+In the Python Table API, a Python table function is used with `.join_lateral`
or `.left_outer_join_lateral`. The `join_lateral` operator (cross) joins each
row from the outer table (table on the left of the operator) with all rows
produced by the table-valued function (which is on the right side of the
operator). The `left_outer_join_lateral` operator joins each row from the outer
table (table on the left of the operator) with all rows produced by the
table-valued function (which is on the right side of the operator) and
preserves outer rows for which the table function returns an empty table. In
SQL use `LATERAL TABLE(<TableFunction>)` with CROSS JOIN and LEFT JOIN with an
ON TRUE join condition (see examples below).
-table_env = BatchTableEnvironment.create(env)
-my_table = ... # type: Table, table schema: [a: String]
+<span class="label label-info">Note</span> Currently, Python UDTF is supported
in old planner both under streaming and batch mode while is only supported
under streaming mode in Blink planner.
-# Register the java function.
-table_env.register_java_function("split", "my.java.function.Split")
+The following example shows how to define a Python table function, registered
it in the TableEnvironment, and call it in a query. Note that you can configure
your table function via a constructor before it is registered:
-# Use the table function in the Python Table API. "as" specifies the field
names of the table.
-my_table.join_lateral("split(a) as (word, length)").select("a, word, length")
-my_table.left_outer_join_lateral("split(a) as (word, length)").select("a,
word, length")
+{% highlight python %}
+class Split(TableFunction):
+ def eval(self, string):
+ for s in string.split(" "):
+ yield s, len(s)
+
+env = StreamExecutionEnvironment.get_execution_environment()
+table_env = StreamTableEnvironment.create(env)
+my_table = ... # type: Table, table schema: [a: String]
-# Register the python function.
+# register the Python Table Function
+table_env.register_function("split", udtf(Split(), DataTypes.STRING(),
[DataTypes.STRING(), DataTypes.INT()]))
-# Use the table function in SQL with LATERAL and TABLE keywords.
-# CROSS JOIN a table function (equivalent to "join" in Table API).
+# use the Python Table Function in Python Table API
+my_table.join_lateral("split(a) as (word, length)")
+my_table.left_outer_join_lateral("split(a) as (word, length)")
+
+# use the Python Table function in SQL API
table_env.sql_query("SELECT a, word, length FROM MyTable, LATERAL
TABLE(split(a)) as T(word, length)")
-# LEFT JOIN a table function (equivalent to "left_outer_join" in Table API).
table_env.sql_query("SELECT a, word, length FROM MyTable LEFT JOIN LATERAL
TABLE(split(a)) as T(word, length) ON TRUE")
+
{% endhighlight %}
+
+There are many ways to define a Python table function besides extending the
base class `TableFunction`.
+Please refer to the [Python Table Function]({{ site.baseurl
}}/dev/table/python/python_udfs.html#table-functions) documentation for more
details.
Review comment:
Change the link to the Chinese doc link, i.e., `zh/dev/`
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