How to use variables in Google BigQuery

Posted by Pascal Landau on 2020-05-29 12:00:00

Variables are a good way to keep a query "clean" and separate parameters from code. In Google BigQuery, we can use variables in standard sql by defining them with a DECLARE statement, e.g.


#DECLARE <variable> <type> DEFAULT <value>;

with <type> being one of the BigQuery's built-in standard-sql data types

This is equivalent to variables of other SQL databases, e.g. - MySQL variables: SET @foo = 'bar'; - PostgreSQL variables: foo varchar := 'bar';



SELECT foo_var

Working Example

Run on BigQuery

Open in BigQuery Console

BigQuery Console: How to declare and use variables example


Use cases

Hardcoding variables is generally considered a bad practice as it makes it harder to understand and modify a query. A frequent use case for me is the definition of date ranges (from and to dates) that are used for querying partitioned tables:

```` DECLARE from_date DATE DEFAULT DATE("2018-04-09"); DECLARE to_date DATE DEFAULT DATE("2018-04-10");

WITH data as( SELECT 1 as id, DATE("2018-04-08") AS date, UNION ALL SELECT 2, DATE("2018-04-09") UNION ALL SELECT 3, DATE("2018-04-10") UNION ALL SELECT 4, DATE("2018-04-11") )

SELECT id, date FROM data WHERE date BETWEEN from_date AND to_date ```

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