SELECT (Stream)

Continuously pulls records from the stream(s) specified. It is usually used in an interactive CLI to monitor realtime changes of data. Note that the query writes records to a random-named stream which is hidden from users.

Synopsis

SELECT <* | expression [ AS field_alias ] [, ...]>
  FROM stream_name [, ...]
  [ WHERE search_condition ]
  [ GROUP BY field_name [, window_type] ]
  EMIT CHANGES;

Notes

• expression can be a field name, a constant, or their association, such as temperature, weather.humidity, 114514, 1 + 2, SUM(productions) and `COUNT(*)`. Note that the last one is a raw column name which is used when a column name contains function names. See Special Characters.
• some_interval represents a period of time. See Intervals.
• window_type specifies the type of time window:

  window_type ::= TUMBLING some_interval
                | HOPPING  some_interval some_interval
                | SLIDING  some_interval
  

• search_condition is actually a boolean expression:

  search_condition ::= [NOT] predicate [ <AND | OR> predicate [, ...] ]
  predicate        ::= expression comp_op expression
  comp_op          ::= = | <> | > | < | >= | <=
  

Examples

• A simple query:

SELECT * FROM my_stream EMIT CHANGES;

• Filtering rows:

SELECT temperature, humidity FROM weather WHERE temperature > 10 AND humidity < 75 EMIT CHANGES;

• Joining streams:

SELECT stream1.temperature, stream2.humidity FROM stream1, stream2 WHERE stream1.humidity = stream2.humidity EMIT CHANGES;

• Grouping records:

SELECT COUNT(*) FROM weather GROUP BY cityId, TUMBLING (INTERVAL 10 SECOND) EMIT CHANGES;