SELECT

The SELECT clause is mandatory and tells RioDB what fields should be gathered when query conditions are met. It also tells RioDB that the intent of your statement is to create a query.

What can you select?

1. Any field from the current message that is passing through the stream, like: my_stock_stream.SYMBOL
   You can use just the field name if it’s not found on multiple sources, like: SYMBOL
   You cannot access fields from past messages. But all fields from the current message are accessible.
2. Any aggregation value from any window in the query data sources (FROM), like: last_10_bids.SUM
   You can just use the aggregation name if it’s not found on multiple sources, like: SUM
   You cannot select an aggregation from a window that is not running that aggregation.
3. Expressions, for example: (SUM – MAX) / 2
4. Scalar functions, like: CONCAT( EXCHANGE, ‘-‘, SYMBOL )
5. Hardcoded values, like: ‘USA’

Syntax

Selected fields are separated by commas. Newlines are ignored, but useful for code readability:

SELECT
  <field 1>,
  <field 2,
  <...>,
  <field n>

Optionally, fields can be given a name:

SELECT
  <field 1> as <name 1>,
  <field 2 as <name 2>,
  <...>,
  <field n> as <name n>
FROM ...

Example

SELECT
  SYMBOL,
  BID,
  (SUM - MAX) / 2,
  CONCAT(EXCHANGE, '-', SYMBOL),
  'USA'
FROM ...

Using field names:

SELECT
  SYMBOL     as stock_symbol,
  BID        as bid_amount,
  (SUM - MAX) / 2                 as computed_ratio,
  CONCAT(EXCHANGE, '-', SYMBOL) as unique_id,
  'USA'      as country
FROM ...