Re: [PR] [FLINK-36941][docs] Update DATE_FORMAT Doc and Python Tests in 1.20 [flink]

["snuyanzin (via GitHub)" <gi...@apache.org>]

snuyanzin commented on code in PR #25874:
URL: https://github.com/apache/flink/pull/25874#discussion_r1905081855


##########
flink-python/pyflink/table/expressions.py:
##########
@@ -350,14 +350,21 @@ def temporal_overlaps(left_time_point,
 def date_format(timestamp, format) -> Expression:
     """
     Formats a timestamp as a string using a specified format.
-    The format must be compatible with MySQL's date formatting syntax as used by the
-    date_parse function.
 
-    For example `date_format(col("time"), "%Y, %d %M")` results in strings formatted as
-    "2017, 05 May".
+    Supported functions:
+    1. date_format(TIMESTAMP, STRING) -> STRING
+    Converts timestamp to a string, using a format string.
+    The format string is compatible with Java's DateTimeFormatter.
+    2. date_format(STRING, STRING) -> STRING
+    Converts timestamp string, using a format string.
+    The format string is compatible with Java's SimpleDateFormat.
+
+    Example:
+    ::
+
+        >>> table.select(date_format(to_timestamp('2020-04-15'), "yyyy/MM/dd"))
+        >>> table.select(date_format("2020-04-15", "MM/dd/yyyy"))

Review Comment:
   IIUC it works only with timestamp string like 
   ```sql
   SELECT date_format('2020-04-15 12:12:12', 'MM/dd/yyyy');
   ```
   
   and for the expression from this PR like 
   ```python
   table.select(date_format("2020-04-15", "MM/dd/yyyy"))
   ```
   it will return `null` 
   I think it is better to provide examples which could return some meaningful output 
   WDYT?



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