Project: Flink (App Definition and Development / Streaming & Messaging)
File: window-join.md

title: "Window JOIN" weight: 10 type: docs <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> {{< label Batch >}} {{< label 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 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. Usually, Window Join is used with . Besides, Window Join could follow after other operations based on , such as , and . {{< hint info >}} Note: `SESSION` Window Join is not supported in batch mode now. {{< /hint >}} Currently, Window Join requires the join on condition contains window starts equality of input tables and window ends equality of input tables. Window Join supports INNER/LEFT/RIGHT/FULL OUTER/ANTI/SEMI JOIN. The following shows the syntax of the INNER/LEFT/RIGHT/FULL OUTER Window Join statement. ```sql SELECT ... FROM L [LEFT|RIGHT|FULL OUTER] JOIN R -- L and R are relations applied windowing TVF ON L.windowstart = R.windowstart AND L.windowend = R.windowend 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

```sql Flink SQL> desc LeftTable; +-+++--+--+-+ | name | type | null | key | extras | watermark | +-+++--+--+-+ | rowtime | TIMESTAMP(3) *ROWTIME* | true | | | `rowtime` - 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 | +-+++--+--+-+ | rowtime | TIMESTAMP(3) *ROWTIME* | true | | | `rowtime` - 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 LNum, L.id as LId, R.num as RNum, R.id as RId, COALESCE(L.windowstart, R.windowstart) as window_start, COALESCE(L.windowend, R.windowend) 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.windowstart = R.windowstart AND L.windowend = R.windowend; +-++-++++ | LNum | LId | RNum | RId | windowstart | windowend | +-++-++++ | 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)`. 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. ```sql 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.windowstart = R.windowstart AND L.windowend = R.windowend); ++--+-+++-+ | rowtime | num | id | windowstart | windowend | windowtime | ++--+-+++-+ | 2020-04-15 12:03 | 3 | L3 | 2020-04-15 12:00 | 2020-04-15 12:05 | 2020-04-15

| ++--+-+++-+ 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.windowstart = R.windowstart AND L.windowend = R.windowend); ++--+-+++-+ | rowtime | num | id | windowstart | windowend | windowtime | ++--+-+++-+ | 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)`. Anti Window Joins are the obverse of the Inner Window Join: they contain all of the unjoined rows within each common window. ```sql 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.windowstart = R.windowstart AND L.windowend = R.windowend); ++--+-+++-+ | rowtime | num | id | windowstart | windowend | windowtime | ++--+-+++-+ | 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.windowstart = R.windowstart AND L.windowend = R.windowend); ++--+-+++-+ | rowtime | num | id | windowstart | windowend | windowtime | ++--+-+++-+ | 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)`. 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. 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. Currently, if Window Join follows after , the has to be with Tumble Windows, Hop Windows or Cumulate Windows instead of Session windows. {{< top >}}