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- Notable SELECT statement behaviors
- Data types and casting operations
- SELECT statement examples
SELECT field_expression[, ..., field_expression_n[, tag_expression[, ..., tag_expression_n]]] FROM measurement_expression[, ..., measurement_expression_n]
SELECT clause supports several formats for identifying data to query.
It requires one or more field expressions and optional tag expressions.
- field_expression: Expression to identify one or more fields to return in query results.
Can be a field key,
constant, regular expression,
*), or function expression and any combination of arithmetic operators.
- tag_expression: Expression to identify one or more tags to return in query results. Can be a tag key or constant.
Select clause behaviors
SELECT field_key- Returns a specific field.
SELECT field_key1, field_key2- Returns two specific fields.
SELECT field_key, tag_key- Returns a specific field and tag.
SELECT *- Returns all fields and tags. See Wildcard expressions.
SELECT /^[t]/- Returns all fields and tags with keys that match the regular expression. At least one field key must match the regular expression. If no field keys match the regular expression, no results are returned.
FROM clause specifies the
measurement to query.
It requires one or more comma-delimited measurement expressions.
Expression to identify one or more measurements to query. Can be a measurement name, fully-qualified measurement, constant, or regular expression.
FROM database.retention_policy.measurement -- Fully-qualified measurement with default retention policy FROM database..measurement
InfluxDB retention policies
In InfluxDB Clustered, retention policies are not part of the data model like they are in InfluxDB 1.x. Each InfluxDB Clustered database has a retention period which defines the maximum age of data to retain in the database. To use fully-qualified measurements in InfluxQL queries, use the following naming convention when creating a database:
Notable SELECT statement behaviors
- Must query at least one field
- Wildcard expressions
- Cannot include both aggregate and non-aggregate field expressions
Must query at least one field
A query requires at least one field key
SELECT clause to return data.
SELECT clause includes only tag keys,
the query returns an empty result.
When using regular expressions in the
SELECT clause, if regular expression
matches only tag keys and no field keys, the query returns an empty result.
To return data associated with tag keys, include at least one field key in the
When using a wildcard expression (
*) in the
SELECT clause, the query returns
all tags and fields.
If a function is
applied to a wildcard expression, the query returns all fields with
the function applied, but does not return tags unless they are included in
Cannot include both aggregate and non-aggregate field expressions
SELECT statement cannot include an aggregate field expression
(one that uses an aggregate
function) and a non-aggregate field expression.
For example, in the following query, an aggregate function is applied to one
field, but not the other:
SELECT mean(temp), hum FROM home
This query returns an error. For more information, see error about mixing aggregate and non-aggregate queries.
Data types and casting operations
SELECT field_expression::type FROM measurement_expression
:: syntax allows users to perform basic cast operations in queries.
Currently, InfluxQL supports casting numeric field values
to other numeric types.
Casting to an identifier type acts as a filter on results and returns only
columns of that specific identifier type along with the
InfluxQL returns no data if the query attempts to cast a numeric value to a non-numeric type and vice versa.
When casting a float value to an integer or unsigned integer, the float value is truncated at the decimal point. No rounding is performed.
SELECT statement examples
The examples below use the following sample data sets:
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