BigQuery query creation without variables? - google-bigquery

Question

Coming from SQL Server and a little bit of MySQL, I'm not sure how to proceed on google's BigQuery web browser query tool.
There doesn't appear to be any way to create, use or Set/Declare variables. How are folks working around this? Or perhaps I have missed something obvious in the instructions or the nature of BigQuery? Java API?

Answer 1

It is now possible to declare and set variables using SQL. For more information, see the documentation, but here is an example:
-- Declare a variable to hold names as an array.
DECLARE top_names ARRAY<STRING>;
-- Build an array of the top 100 names from the year 2017.
SET top_names = (
SELECT ARRAY_AGG(name ORDER BY number DESC LIMIT 100)
FROM `bigquery-public-data`.usa_names.usa_1910_current
WHERE year = 2017
);
-- Which names appear as words in Shakespeare's plays?
SELECT
name AS shakespeare_name
FROM UNNEST(top_names) AS name
WHERE name IN (
SELECT word
FROM `bigquery-public-data`.samples.shakespeare
);

Answer 2

There is currently no way to set/declare variables in BigQuery. If you need variables, you'll need to cut and paste them where you need them. Feel free to file this as a feature request here.

Answer 3

Its not elegant, and its a a pain, but...
The way we handle it is using a python script that replaces a "variable placeholder" in our query and than sending the amended query via the API.
I have opened a feature request asking for "Dynamic SQL" capabilities.

Answer 4

If you want to avoid BQ scripting, you can sometimes use an idiom which utilizes WITH and CROSS JOIN.
In the example below:
the events table contains some timestamped events
the reports table contain occasional aggregate values of the events
the goal is to write a query that only generates incremental (non-duplicate) aggregate rows
This is achieved by
introducing a state temp table that looks at a target table for aggregate results
to determine parameters (params) for the actual query
the params are CROSS JOINed with the actual query
allowing the param row's columns to be used to constrain the query
this query will repeatably return the same results
until the results themselves are appended to the reports table
WTIH state AS (
SELECT
-- what was the newest report's ending time?
COALESCE(
SELECT MAX(report_end_ts) FROM `x.y.reports`,
TIMESTAMP("2019-01-01")
) AS latest_report_ts,
...
),
params AS (
SELECT
-- look for events since end of last report
latest_report_ts AS event_after_ts,
-- and go until now
CURRENT_TIMESTAMP() AS event_before_ts
)
SELECT
MIN(event_ts) AS report_begin_ts,
MAX(event_ts) AS report_end_ts
COUNT(1) AS event_count,
SUM(errors) AS error_total
FROM `x.y.events`
CROSS JOIN params
WHERE event_ts > event_after_ts
AND event_ts < event_before_ts
)
This approach is useful for bigquery scheduled queries.