窗口关联

窗口关联 #

Batch Streaming

窗口关联就是增加时间维度到关联条件中。在此过程中,窗口关联将两个流中在同一窗口且符合 join 条件的元素 join 起来。窗口关联的语义和 DataStream window join 相同。

在流式查询中,与其他连续表上的关联不同,窗口关联不产生中间结果,只在窗口结束产生一个最终的结果。另外,窗口关联会清除不需要的中间状态。

通常,窗口关联和 窗口表值函数 一起使用。而且,窗口关联可以在其他基于 窗口表值函数 的操作后使用,例如 窗口聚合窗口 Top-N窗口关联

目前,窗口关联需要在 join on 条件中包含两个输入表的 window_start 等值条件和 window_end 等值条件。

窗口关联支持 INNER/LEFT/RIGHT/FULL OUTER/ANTI/SEMI JOIN。

INNER/LEFT/RIGHT/FULL OUTER #

下面展示了 INNER/LEFT/RIGHT/FULL OUTER 窗口关联的语法:

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 ...

INNER/LEFT/RIGHT/FULL OUTER 这几种窗口关联的语法非常相似,我们在这里只举一个 FULL OUTER JOIN 的例子。 当执行窗口关联时,所有具有相同 key 和相同滚动窗口的数据会被关联在一起。这里给出一个基于 TUMBLE Window TVF 的窗口连接的例子。 在下面的例子中,通过将 join 的时间区域限定为固定的 5 分钟,数据集被分成两个不同的时间窗口:[12:00,12:05) 和 [12:05,12:10)。L2 和 R2 不能 join 在一起是因为它们不在一个窗口中。

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,
           COALESCE(L.window_start, R.window_start) as window_start,
           COALESCE(L.window_end, R.window_end) as 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 |
+-------+------+-------+------+------------------+------------------+

注意:为了更好地理解窗口行为,这里把 timestamp 值后面的 0 去掉了。例如:在 Flink SQL Client 中,如果类型是 TIMESTAMP(3)2020-04-15 08:05 应该显示成 2020-04-15 08:05:00.000

SEMI #

如果在同一个窗口中,左侧记录在右侧至少有一个匹配的记录时,半窗口连接(Semi Window Join)就会输出左侧的记录。

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 |
+------------------+-----+----+------------------+------------------+-------------------------+

注意:为了更好地理解窗口行为,这里把 timestamp 值后面的 0 去掉了。例如:在 Flink SQL Client 中,如果类型是 TIMESTAMP(3)2020-04-15 08:05 应该显示成 2020-04-15 08:05:00.000

ANTI #

反窗口连接(Anti Window Join)是内窗口连接(Inner Window Join)的相反操作:它包含了每个公共窗口内所有未关联上的行。

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 |
+------------------+-----+----+------------------+------------------+-------------------------+

注意:为了更好地理解窗口行为,这里把 timestamp 值后面的 0 去掉了。例如:在 Flink SQL Client 中,如果类型是 TIMESTAMP(3)2020-04-15 08:05 应该显示成 2020-04-15 08:05:00.000

限制 #

Join 子句的限制 #

目前,窗口关联需要在 join on 条件中包含两个输入表的 window_start 等值条件和 window_end 等值条件。未来,如果是滚动或滑动窗口,只需要在 join on 条件中包含窗口开始相等即可。

输入的窗口表值函数的限制 #

目前,关联的左右两边必须使用相同的窗口表值函数。这个规则在未来可以扩展,比如:滚动和滑动窗口在窗口大小相同的情况下 join。

窗口表值函数之后直接使用窗口关联的限制 #

目前窗口关联支持作用在滚动(TUMBLE)、滑动(HOP)和累积(CUMULATE)窗口表值函数 之上,但是还不支持会话窗口(SESSION)。

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