UNION clause
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.
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
SELECT expression[,...n]
FROM measurement_1
UNION [ALL]
SELECT expression[,...n]
FROM measurement_2
Examples
- Union results from different measurements
- Return the highest and lowest three results in a single result set
- Union query results with custom data
Union results from different measurements
(
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
)
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.
(
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
)
Union query results with custom data
The following example uses the sample data set provided in Get started with InfluxDB tutorial. It also uses the table value constructor to build a table with custom data.
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
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