Select statements are used to manipulate data in Arroyo.``` The general form of that statement is:
[WITH with_query [, ...]] SELECT select_expr [, ...] FROM from_item [JOIN join_item [, ...]] [WHERE condition] [GROUP BY grouping_element [, ...]]
The with clauses allow you to give names to subquery which you can then reference. The syntax for a with clause is:
WITH query_name AS (subquery) [,...]
For example, using the nexmark source, you can create datasets for bids and price and then join.
WITH bids AS (SELECT bid.auction AS auction, bid.price AS price FROM nexmark where bid is not null), auctions AS (SELECT auction.id AS id FROM nexmark where auction is not null) SELECT * FROM bids bids JOIN auctions auctions ON bids.auction = auctions.id;
The select cause is a comma-separated list of expressions, with an optional alias.
Column names must be unique.
SELECT select_expr [, ...]
FROM clause specifies the primary source of data.
It will be either a table name or subquery.
The table name can be either a saved source,
a table created in the
WITH clause or a table created via
CREATE TABLE and inserted into.
Tables can be given aliases, but will default to their name as the alias for things like joins.
JOIN clause allows you to join multiple tables together.
By default it will be an inner join, but you can also specify
Joins must include an
ON clause specifying the join condition.
SELECT * FROM bids join auctions on bids.auction = auctions.id;
WHERE clause allows you to filter the data with a boolean condition.
This predicate is applied to the incoming rows, so cannot include conditions on the resulting columns.
GROUP BY clause
GROUP BY clause is used to compute aggregates over some set of fields.
All GROUP BY queries will implicitly include a time window,
and if the input doesn’t already have a time window,
it should be specified as one of the grouping fields.
SELECT count(*) AS bids, count(distinct auction_id) AS distinct_auctions, tumble(interval '1 minute') AS window FROM BIDS GROUP BY 3
UNNEST operator allows you to unnest arrays into multiple rows. This can be used
as a normal scalar function with the following restrictions:
- It may only appear in the
- Only one array may be unnested per select statement For example,
SELECT UNNEST(make_array(1, 2, 3)) as x FROM BIDS;
which will produce the following output:
+---+ | x | +---+ | 1 | | 2 | | 3 | +---+