Fluent Bit + SQL

Fluent Bit stream processor uses common SQL to perform record queries. The following section describe the features available and examples of it.
Statements
You can find the detailed query language syntax in BNF form here. The following section will be a brief introduction on how to write SQL queries for Fluent Bit stream processing.
SELECT Statement
Synopsis
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SELECT results_statement
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  FROM STREAM:stream_name | TAG:match_rule
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  [WINDOW TUMBLING (integer SECOND)]
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  [WHERE condition]
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  [GROUP BY groupby]
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Description
Select keys from records coming from a stream or records matching a specific Tag pattern. Note that a simple SELECT statement not associated from a stream creation will send the results to the standard output interface (stdout), useful for debugging purposes.
The query allows filtering the results by applying a condition using WHERE statement. We will explain WINDOW and GROUP BY statements later in aggregation functions section.
Examples
Select all keys from records coming from a stream called apache:
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SELECT * FROM STREAM:apache;
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Select code key from records which Tag starts with apache.:
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SELECT code AS http_status FROM TAG:'apache.*';
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Since the TAG selector allows the use of wildcards, we put the value between single quotes.
CREATE STREAM Statement
Synopsis
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CREATE STREAM stream_name
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  [WITH (property_name=value, [...])]
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  AS select_statement
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Description
Create a new stream of data using the results from the SELECT statement. New stream created can be optionally re-ingested back into Fluent Bit pipeline if the property Tag is set in the WITH statement.
Examples
Create a new stream called hello from stream called apache:
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CREATE STREAM hello AS SELECT * FROM STREAM:apache;
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Create a new stream called hello for all records which original Tag starts with apache:
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CREATE STREAM hello AS SELECT * FROM TAG:'apache.*';
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Aggregation Functions
Aggregation functions are used in results_statement on the keys, allowing to perform data calculation on groups of records. Group of records that aggregation functions apply on are determined by WINDOW keyword. When WINDOW is not specified, aggregation functions apply on the current buffer of records received, which may have non-deterministic number of elements. Aggregation functions can be applied on records in a window of a specific time interval (see the syntax of WINDOW in select statement).
Fluent Bit streaming currently supports tumbling window, which is non-overlapping window type. That means, a window of size 5 seconds performs aggregation computations on records over a 5-second interval, and then starts new calculations for the next interval.
In addition, the syntax support GROUP BY statement, which groups the results by the one or more keys, when they have the same values.
AVG
Synopsis
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SELECT AVG(size) FROM STREAM:apache WHERE method = 'POST' ;
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Description
Calculates the average of request sizes in POST requests.
COUNT
Synopsis
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SELECT host, COUNT(*) FROM STREAM:apache WINDOW TUMBLING (5 SECOND) GROUP BY host;
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Description
Count the number of records in 5 second windows group by host IP addresses.
MIN
Synopsis
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SELECT MIN(key) FROM STREAM:apache;
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Description
Gets the minimum value of a key in a set of records.
MAX
Synopsis
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SELECT MIN(key) FROM STREAM:apache;
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Description
Gets the maximum value of a key in a set of records.
SUM
Synopsis
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SELECT SUM(key) FROM STREAM:apache;
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Description
Calculates the sum of all values of key in a set of records.
Time Functions
Time functions adds a new key into the record with timing data
NOW
Synopsis
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SELECT NOW() FROM STREAM:apache;
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Description
Add system time using format: %Y-%m-%d %H:%M:%S. Output example: 2019-03-09 21:36:05.
UNIX_TIMESTAMP
Synopsis
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SELECT UNIX_TIMESTAMP() FROM STREAM:apache;
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Description
Add current Unix timestamp to the record. Output example: 1552196165 .
Record Functions
Record functions append new keys to the record using values from the record context.
RECORD_TAG
Synopsis
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SELECT RECORD_TAG() FROM STREAM:apache;
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Description
Append Tag string associated to the record as a new key.
RECORD_TIME
Synopsis
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SELECT RECORD_TIME() FROM STREAM:apache;
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WHERE Condition
Similar to conventional SQL statements, WHERE condition is supported in Fluent Bit query language. The language supports conditions over keys and subkeys, for instance:
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SELECT AVG(size) FROM STREAM:apache WHERE method = 'POST' AND status = 200;
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It is possible to check the existence of a key in the record using record-specific function @record.contains:
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SELECT MAX(key) FROM STREAM:apache WHERE @record.contains(key);
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And to check if the value of a key is/is not NULL:
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SELECT MAX(key) FROM STREAM:apache WHERE key IS NULL;
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SELECT * FROM STREAM:apache WHERE user IS NOT NULL;
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Description
Append a new key with the record Timestamp in double format: seconds.nanoseconds. Output example: 1552196165.705683 .