Flink SQL:Queries(Window JOIN)

Window Join

Batch Streaming

A window join adds the dimension of time into the join criteria themselves. In doing so, the window join joins the elements of two streams that share a common key and are in the same window. The semantic of window join is same to the DataStream window join
窗口join将时间维度添加到连接条件本身。在这样做的过程中，窗口join将两个流的元素连接起来，这两个流共享一个公共key并且位于同一个窗口中。窗口join的语义与DataStream窗口join相同

For streaming queries, unlike other joins on continuous tables, window join does not emit intermediate results but only emits final results at the end of the window. Moreover, window join purge all intermediate state when no longer needed.
对于流式查询，与持续表上的其他join不同，窗口join不发出中间结果，而只在窗口末尾发出最终结果。此外，窗口join在不再需要时清除所有中间状态。

Usually, Window Join is used with Windowing TVF. Besides, Window Join could follow after other operations based on Windowing TVF, such as Window Aggregation, Window TopN and Window Join.
通常，窗口Join与Windowing TVF一起使用。此外，窗口Join还可以跟随基于Windowing TVF的其他操作，如Window Aggregation、Window TopN和Window Join。

Currently, Window Join requires the join on condition contains window starts equality of input tables and window ends equality of input tables.
当前，窗口join要求连接条件包含:输入表的窗口开始相等且输出表的窗口结束相等。

Window Join supports INNER/LEFT/RIGHT/FULL OUTER/ANTI/SEMI JOIN.
窗口Join支持INNER/LEFT/RIGHT/FULL OUTER/ANTI/SEMI JOIN。

INNER/LEFT/RIGHT/FULL OUTER

The following shows the syntax of the INNER/LEFT/RIGHT/FULL OUTER Window Join statement.
下面显示 INNER/LEFT/RIGHT/FULL OUTER Window Join语句的语法。

SELECT ...
FROM L [LEFT|RIGHT|FULL OUTER] JOIN R -- L and R are relations applied windowing TVF
ON L.window_start = R.window_start AND L.window_end = R.window_end AND ...

The syntax of INNER/LEFT/RIGHT/FULL OUTER WINDOW JOIN are very similar with each other, we only give an example for FULL OUTER JOIN here. When performing a window join, all elements with a common key and a common tumbling window are joined together. We only give an example for a Window Join which works on a Tumble Window TVF. By scoping the region of time for the join into fixed five-minute intervals, we chopped our datasets into two distinct windows of time: [12:00, 12:05) and [12:05, 12:10). The L2 and R2 rows could not join together because they fell into separate windows.
INNER/LEFT/RIGHT/FULL OUTER WINDOW JOIN的语法非常相似，我们在这里只给出一个FULL OUTER JOIN示例。执行窗口join时，具有公共key和公共滚动窗口的所有元素都将连接在一起。我们只给出了一个在Tumble Window TVF上工作的窗口join示例。通过将join的时间区域划分为固定的5分钟间隔，我们将数据集分割为两个不同的时间窗口：[12:00，12:05）和[12:05，12:10）。L2和R2行无法连接在一起，因为它们属于不同的窗口。

Flink SQL> desc LeftTable;
+----------+------------------------+------+-----+--------+----------------------------------+
|     name |                   type | null | key | extras |                        watermark |
+----------+------------------------+------+-----+--------+----------------------------------+
| row_time | TIMESTAMP(3) *ROWTIME* | true |     |        | `row_time` - INTERVAL '1' SECOND |
|      num |                    INT | true |     |        |                                  |
|       id |                 STRING | true |     |        |                                  |
+----------+------------------------+------+-----+--------+----------------------------------+

Flink SQL> SELECT * FROM LeftTable;
+------------------+-----+----+
|         row_time | num | id |
+------------------+-----+----+
| 2020-04-15 12:02 |   1 | L1 |
| 2020-04-15 12:06 |   2 | L2 |
| 2020-04-15 12:03 |   3 | L3 |
+------------------+-----+----+

Flink SQL> desc RightTable;
+----------+------------------------+------+-----+--------+----------------------------------+
|     name |                   type | null | key | extras |                        watermark |
+----------+------------------------+------+-----+--------+----------------------------------+
| row_time | TIMESTAMP(3) *ROWTIME* | true |     |        | `row_time` - INTERVAL '1' SECOND |
|      num |                    INT | true |     |        |                                  |
|       id |                 STRING | true |     |        |                                  |
+----------+------------------------+------+-----+--------+----------------------------------+

Flink SQL> SELECT * FROM RightTable;
+------------------+-----+----+
|         row_time | num | id |
+------------------+-----+----+
| 2020-04-15 12:01 |   2 | R2 |
| 2020-04-15 12:04 |   3 | R3 |
| 2020-04-15 12:05 |   4 | R4 |
+------------------+-----+----+

Flink SQL> SELECT L.num as L_Num, L.id as L_Id, R.num as R_Num, R.id as R_Id, L.window_start, L.window_end
           FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE LeftTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) L
           FULL JOIN (
               SELECT * FROM TABLE(TUMBLE(TABLE RightTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) R
           ON L.num = R.num AND L.window_start = R.window_start AND L.window_end = R.window_end;
+-------+------+-------+------+------------------+------------------+
| L_Num | L_Id | R_Num | R_Id |     window_start |       window_end |
+-------+------+-------+------+------------------+------------------+
|     1 |   L1 |  null | null | 2020-04-15 12:00 | 2020-04-15 12:05 |
|  null | null |     2 |   R2 | 2020-04-15 12:00 | 2020-04-15 12:05 |
|     3 |   L3 |     3 |   R3 | 2020-04-15 12:00 | 2020-04-15 12:05 |
|     2 |   L2 |  null | null | 2020-04-15 12:05 | 2020-04-15 12:10 |
|  null | null |     4 |   R4 | 2020-04-15 12:05 | 2020-04-15 12:10 |
+-------+------+-------+------+------------------+------------------+

Note: in order to better understand the behavior of windowing, we simplify the displaying of timestamp values to not show the trailing zeros, e.g. 2020-04-15 08:05 should be displayed as 2020-04-15 08:05:00.000 in Flink SQL Client if the type is TIMESTAMP(3).
注意：为了更好地理解窗口化的行为，我们简化了时间戳值的显示，以不显示尾随的零，例如，如果类型为TIMESTAMP(3)，则在Flink SQL Client中，2020-04-15 08:05应显示为2020-04-14 08:05:00.000。

SEMI

Semi Window Joins returns a row from one left record if there is at least one matching row on the right side within the common window.
如果公共窗口中右侧至少有一个匹配行，则Semi Window Joins将从左边的记录返回一行。

Flink SQL> SELECT *
           FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE LeftTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) L WHERE L.num IN (
             SELECT num FROM (   
               SELECT * FROM TABLE(TUMBLE(TABLE RightTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
             ) R WHERE L.window_start = R.window_start AND L.window_end = R.window_end);
+------------------+-----+----+------------------+------------------+-------------------------+
|         row_time | num | id |     window_start |       window_end |            window_time  |
+------------------+-----+----+------------------+------------------+-------------------------+
| 2020-04-15 12:03 |   3 | L3 | 2020-04-15 12:00 | 2020-04-15 12:05 | 2020-04-15 12:04:59.999 |
+------------------+-----+----+------------------+------------------+-------------------------+

Flink SQL> SELECT *
           FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE LeftTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) L WHERE EXISTS (
             SELECT * FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE RightTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
             ) R WHERE L.num = R.num AND L.window_start = R.window_start AND L.window_end = R.window_end);
+------------------+-----+----+------------------+------------------+-------------------------+
|         row_time | num | id |     window_start |       window_end |            window_time  |
+------------------+-----+----+------------------+------------------+-------------------------+
| 2020-04-15 12:03 |   3 | L3 | 2020-04-15 12:00 | 2020-04-15 12:05 | 2020-04-15 12:04:59.999 |
+------------------+-----+----+------------------+------------------+-------------------------+

Note: in order to better understand the behavior of windowing, we simplify the displaying of timestamp values to not show the trailing zeros, e.g. 2020-04-15 08:05 should be displayed as 2020-04-15 08:05:00.000 in Flink SQL Client if the type is TIMESTAMP(3).
注意：为了更好地理解窗口化的行为，我们简化了时间戳值的显示，以不显示尾随的零，例如，如果类型为TIMESTAMP(3)，则在Flink SQL Client中，2020-04-15 08:05应显示为2020-04-14 08:05:00.000。

ANTI

Anti Window Joins are the obverse of the Inner Window Join: they contain all of the unjoined rows within each common window.
Anti窗口join是Inner窗口join的对立面：包含每个公共窗口中所有未连接的行。

Flink SQL> SELECT *
           FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE LeftTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) L WHERE L.num NOT IN (
             SELECT num FROM (   
               SELECT * FROM TABLE(TUMBLE(TABLE RightTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
             ) R WHERE L.window_start = R.window_start AND L.window_end = R.window_end);
+------------------+-----+----+------------------+------------------+-------------------------+
|         row_time | num | id |     window_start |       window_end |            window_time  |
+------------------+-----+----+------------------+------------------+-------------------------+
| 2020-04-15 12:02 |   1 | L1 | 2020-04-15 12:00 | 2020-04-15 12:05 | 2020-04-15 12:04:59.999 |
| 2020-04-15 12:06 |   2 | L2 | 2020-04-15 12:05 | 2020-04-15 12:10 | 2020-04-15 12:09:59.999 |
+------------------+-----+----+------------------+------------------+-------------------------+

Flink SQL> SELECT *
           FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE LeftTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
           ) L WHERE NOT EXISTS (
             SELECT * FROM (
               SELECT * FROM TABLE(TUMBLE(TABLE RightTable, DESCRIPTOR(row_time), INTERVAL '5' MINUTES))
             ) R WHERE L.num = R.num AND L.window_start = R.window_start AND L.window_end = R.window_end);
+------------------+-----+----+------------------+------------------+-------------------------+
|         row_time | num | id |     window_start |       window_end |            window_time  |
+------------------+-----+----+------------------+------------------+-------------------------+
| 2020-04-15 12:02 |   1 | L1 | 2020-04-15 12:00 | 2020-04-15 12:05 | 2020-04-15 12:04:59.999 |
| 2020-04-15 12:06 |   2 | L2 | 2020-04-15 12:05 | 2020-04-15 12:10 | 2020-04-15 12:09:59.999 |
+------------------+-----+----+------------------+------------------+-------------------------+

Note: in order to better understand the behavior of windowing, we simplify the displaying of timestamp values to not show the trailing zeros, e.g. 2020-04-15 08:05 should be displayed as 2020-04-15 08:05:00.000 in Flink SQL Client if the type is TIMESTAMP(3).
注意：为了更好地理解窗口化的行为，我们简化了时间戳值的显示，以不显示尾随的零，例如，如果类型为TIMESTAMP(3)，则在Flink SQL Client中，2020-04-15 08:05应显示为2020-04-14 08:05:00.000。

Limitation

Limitation on Join clause

Currently, The window join requires the join on condition contains window starts equality of input tables and window ends equality of input tables. In the future, we can also simplify the join on clause to only include the window start equality if the windowing TVF is TUMBLE or HOP.
目前，窗口join要求连接条件包含:输入表的窗口开始相等且输出表的窗口结束相等。将来，如果窗口化TVF是TUMBLE或HOP，我们还可以简化join-on子句，使其仅包含窗口开始相等。

Limitation on windowing TVFs of inputs

Currently, the windowing TVFs must be the same of left and right inputs. This can be extended in the future, for example, tumbling windows join sliding windows with the same window size.
目前，左右输入的窗口化TVF必须相同。这在将来可以扩展，例如，滚动窗口连接具有相同窗口大小的滑动窗口。

Limitation on Window Join which follows after Windowing TVFs directly

Currently, if Window Join follows after Windowing TVF, the Windowing TVF has to be with Tumble Windows, Hop Windows or Cumulate Windows instead of Session windows.
目前，如果Window Join跟随在Windowing TVF之后，则Windowing TVF必须使用Tumble Windows、Hop Windows或Cumulate Windows，而不是Session窗口。