[new]: `get_ga4_param(param_name, event_params)`

[unytics]

Check the idea has not already been suggested

• I could not find my idea in existing issues

Edit the title above with self-explanatory function name and argument names

• The function name and the argument names I entered in the title above seems self explanatory to me.

BigFunction Description as it would appear in the documentation

Objective: simplify the following:
https://developers.google.com/analytics/bigquery/basic-queries#values_for_a_specific_event_name

Alejandro Zielinsky proposed the following.

• https://zielinsky.alejand.ro/querying-ga4-event-parameters-in-bigquery-with-function-9f75eb0a2f89
• https://gist.github.com/ZordnajelA/b3c519559a1524d420237c63d5228bc5

From my point of view, we could return the value directly and not a struct with type and value.

Examples of (arguments, expected output) as they would appear in the documentation