SQL UNION documentation (#4716)

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2023-03-08 15:07:33 -06:00 · 2023-03-08 15:07:33 -06:00 · 366c39467c
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+---
+title: UNION clause
+description: > 
+  The `UNION` clause combines the results of two or more `SELECT` statements into
+  a single result set.
+menu:
+  influxdb_cloud_iox:
+    name: UNION clause
+    parent: SQL reference
+weight: 206
+---
+
+The `UNION` clause combines the results of two or more `SELECT` statements into
+a single result set.
+By default, `UNION` only keeps unique rows.
+To keep all rows, including duplicates, use `UNION ALL`.
+
+- [Syntax](#syntax)
+- [Examples](#examples)
+
+**When using the `UNION` clause**:
+
+- The number of columns in each result set must be the same.
+- Columns must be in the same order and of the same or compatible data types.
+
+## Syntax
+
+```sql
+SELECT expression[,...n]
+FROM measurement_1
+UNION [ALL]
+SELECT expression[,...n]
+FROM measurement_2
+```
+
+## Examples
+
+- [Union results from different measurements](#union-results-from-different-measurements)
+- [Return the highest and lowest three results in a single result set](#return-the-highest-and-lowest-three-results-in-a-single-result-set)
+- [Union query results with custom data](#union-query-results-with-custom-data)
+
+### Union results from different measurements
+
+```sql
+(
+  SELECT
+    'h2o_pH' AS measurement,
+    time,
+    "pH" AS "water_pH"
+  FROM "h2o_pH"
+  LIMIT 4
+)
+UNION
+(
+  SELECT
+    'h2o_quality' AS measurement,
+    time,
+    index
+  FROM h2o_quality
+  LIMIT 4
+)
+```
+{{< expand-wrapper >}}
+{{% expand "View example results" %}}
+
+| measurement | time                 | water_pH |
+| :---------- | :------------------- | -------: |
+| h2o_pH      | 2019-08-27T00:12:00Z |        7 |
+| h2o_pH      | 2019-08-27T00:18:00Z |        8 |
+| h2o_quality | 2019-09-11T01:06:00Z |       89 |
+| h2o_pH      | 2019-08-27T00:06:00Z |        7 |
+| h2o_quality | 2019-09-11T00:00:00Z |       26 |
+| h2o_quality | 2019-09-11T01:00:00Z |       19 |
+| h2o_quality | 2019-09-11T00:48:00Z |       65 |
+| h2o_pH      | 2019-08-27T00:00:00Z |        8 |
+
+{{% /expand %}}
+{{< /expand-wrapper >}}
+
+### Return the highest and lowest three results in a single result set
+
+_The following example uses the sample data set provided in
+[Get started with InfluxDB tutorial](/influxdb/cloud-iox/get-started/write/#construct-line-protocol)._
+
+```sql
+(
+  SELECT
+    'low' as type,
+    time,
+    co
+  FROM home
+  ORDER BY co ASC
+  LIMIT 3
+)
+UNION 
+(
+  SELECT
+    'high' as type,
+    time,
+    co
+  FROM home
+  ORDER BY co DESC
+  LIMIT 3
+)
+```
+
+{{< expand-wrapper >}}
+{{% expand "View example results" %}}
+
+| type | time                 |  co |
+| :--- | :------------------- | --: |
+| high | 2022-01-01T20:00:00Z |  26 |
+| high | 2022-01-01T19:00:00Z |  22 |
+| high | 2022-01-01T18:00:00Z |  18 |
+| low  | 2022-01-01T14:00:00Z |   0 |
+| low  | 2022-01-01T10:00:00Z |   0 |
+| low  | 2022-01-01T08:00:00Z |   0 |
+
+{{% /expand %}}
+{{< /expand-wrapper >}}
+
+### Union query results with custom data
+
+_The following example uses the sample data set provided in
+[Get started with InfluxDB tutorial](/influxdb/cloud-iox/get-started/write/#construct-line-protocol).
+It also uses the [table value constructor](/influxdb/cloud-iox/reference/sql/table-value-constructor/)
+to build a table with custom data._
+
+```sql
+SELECT *
+FROM home
+WHERE
+  time >= '2022-01-01T08:00:00Z'
+  AND time <= '2022-01-01T12:00:00Z'
+UNION
+SELECT * FROM
+  (VALUES (0, 34.2, 'Bedroom', 21.1, '2022-01-01T08:00:00Z'::TIMESTAMP),
+          (0, 34.5, 'Bedroom', 21.2, '2022-01-01T09:00:00Z'::TIMESTAMP),
+          (0, 34.6, 'Bedroom', 21.5, '2022-01-01T10:00:00Z'::TIMESTAMP),
+          (0, 34.5, 'Bedroom', 21.8, '2022-01-01T11:00:00Z'::TIMESTAMP),
+          (0, 33.9, 'Bedroom', 22.0, '2022-01-01T12:00:00Z'::TIMESTAMP)
+  ) newRoom(co, hum, room, temp, time)
+ORDER BY room, time
+```
+
+{{< expand-wrapper >}}
+{{% expand "View example results" %}}
+
+|  co |  hum | room        | temp | time                 |
+| --: | ---: | :---------- | ---: | :------------------- |
+|   0 | 34.2 | Bedroom     | 21.1 | 2022-01-01T08:00:00Z |
+|   0 | 34.5 | Bedroom     | 21.2 | 2022-01-01T09:00:00Z |
+|   0 | 34.6 | Bedroom     | 21.5 | 2022-01-01T10:00:00Z |
+|   0 | 34.5 | Bedroom     | 21.8 | 2022-01-01T11:00:00Z |
+|   0 | 33.9 | Bedroom     |   22 | 2022-01-01T12:00:00Z |
+|   0 | 35.9 | Kitchen     |   21 | 2022-01-01T08:00:00Z |
+|   0 | 36.2 | Kitchen     |   23 | 2022-01-01T09:00:00Z |
+|   0 | 36.1 | Kitchen     | 22.7 | 2022-01-01T10:00:00Z |
+|   0 |   36 | Kitchen     | 22.4 | 2022-01-01T11:00:00Z |
+|   0 |   36 | Kitchen     | 22.5 | 2022-01-01T12:00:00Z |
+|   0 | 35.9 | Living Room | 21.1 | 2022-01-01T08:00:00Z |
+|   0 | 35.9 | Living Room | 21.4 | 2022-01-01T09:00:00Z |
+|   0 |   36 | Living Room | 21.8 | 2022-01-01T10:00:00Z |
+|   0 |   36 | Living Room | 22.2 | 2022-01-01T11:00:00Z |
+|   0 | 35.9 | Living Room | 22.2 | 2022-01-01T12:00:00Z |
+
+{{% /expand %}}
+{{< /expand-wrapper >}}