03_group_by.md

03 Aggregating Data

💡 This example will show how to aggregate server logs in real-time using the standard GROUP BY clause.

The source table (server_logs) is backed by the faker connector, which continuously generates rows in memory based on Java Faker expressions.

To count the number of logs received per browser for each status code over time, you can combine the COUNT aggregate function with a GROUP BY clause. Because the user_agent field contains a lot of information, you can extract the browser using the built-in string function REGEXP_EXTRACT.

A GROUP BY on a streaming table produces an updating result, so you will see the aggregated count for each browser continuously changing as new rows flow in.

As an exercise, you can play around with other standard SQL aggregate functions (e.g. SUM,AVG,MIN,MAX).

Script

CREATE TABLE server_logs ( 
    client_ip STRING,
    client_identity STRING, 
    userid STRING, 
    user_agent STRING,
    log_time TIMESTAMP(3),
    request_line STRING, 
    status_code STRING, 
    size INT
) WITH (
  'connector' = 'faker', 
  'fields.client_ip.expression' = '#{Internet.publicIpV4Address}',
  'fields.client_identity.expression' =  '-',
  'fields.userid.expression' =  '-',
  'fields.user_agent.expression' = '#{Internet.userAgentAny}',
  'fields.log_time.expression' =  '#{date.past ''15'',''5'',''SECONDS''}',
  'fields.request_line.expression' = '#{regexify ''(GET|POST|PUT|PATCH){1}''} #{regexify ''(/search\.html|/login\.html|/prod\.html|cart\.html|/order\.html){1}''} #{regexify ''(HTTP/1\.1|HTTP/2|/HTTP/1\.0){1}''}',
  'fields.status_code.expression' = '#{regexify ''(200|201|204|400|401|403|301){1}''}',
  'fields.size.expression' = '#{number.numberBetween ''100'',''10000000''}'
);

-- Sample user_agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
-- Regex pattern: '[^\/]+' (Match everything before '/')
SELECT 
  REGEXP_EXTRACT(user_agent,'[^\/]+') AS browser,
  status_code, 
  COUNT(*) AS cnt_status
FROM server_logs
GROUP BY 
  REGEXP_EXTRACT(user_agent,'[^\/]+'),
  status_code;

Example Output

This example can be run in the SQL Client, a command line tool to develop and execute Flink SQL queries that is bundled in Flink.