Conditionally LIMIT in BigQuery - google-bigquery

Question

I have read that in Postgres setting LIMIT NULL will effectively not limit the results of the SELECT. However in BigQuery when I set LIMIT NULL based on a condition I see Syntax error: Unexpected keyword NULL.
I'd like to figure out a way to limit or not based on a condition (could be an argument passed into a procedure, or a parameter passed in by a query job, anything I can write a CASE or IF statement for). The mechanism for setting the condition shouldn't matter, what I'm looking for is whether there is a way to syntactically indicate a value for LIMIT, that will not limit, in a valid way to BigQuery.

Answer 1

The LIMIT clause works differently within BigQuery. It specifies the maximum number of depression inputs in the result. The LIMIT n must be a constant INT64.
Using the LIMIT clause, you can overcome the limitation on cache result size:
Using filters to limit the result set.
Using a LIMIT clause to reduce the result set, especially if you are
using an ORDER BY clause.
You can see this example:
SELECT
title
FROM
`my-project.mydataset.mytable`
ORDER BY
title DESC
LIMIT
100
This will only return 100 rows.
The best practice is to use it if you are sorting a very large number of values. You can see this document with examples.
If you want to return all rows from a table, you need to omit the LIMIT clause.
SELECT
title
FROM
`my-project.mydataset.mytable`
ORDER BY
title DESC
This example will return all the rows from a table. It is not recommended to omit LIMIT if your tables are too large, as it will consume a lot of resources.
One solution to optimize resources is to use cluster tables. This will save costs and querying times. You can see this document with a detailed explanation of how it works.

Answer 2

You can write a stored procedure that dynamically creates a query based on input parameters. Once your sql query is ready, you can use execute immediate to run that. In this way, you can control what value should be provided to the limit clause of your query.
https://cloud.google.com/bigquery/docs/reference/standard-sql/scripting#execute_immediate
Hope this answers your query.