Mapbox expression to return greater of two values

Question

I'm looking to plot the equivalent of the SQL query

SELECT column_3
FROM my_object
WHERE map_layer is not null
AND column_1 > column_2;

Using this answer I can see where the expression should go (in the filter) and that I can combine multiple filters but not how to compare values.

Which gives me

"source-layer": "my_object",
        "filter": ['all',["==", ["typeof", ["get", "col_3"]], "string"],[another expression here]]

Answer 1

I would interpret 'greater of two values' as the (PG) SQL equivalent of

SELECT GREATEST(column_1, column_2)
...

However, the query you posted would simply translate to

"filter": [">", ["get", "column_1"], ["get", "column_2"]]

or

"filter": [
  "all", 
  ["!=", ["get", "map_layer"], "<NULL_VALUE>"],
  [">", ["get", "column_1"], ["get", "column_2"]
]

filter for (show only) all features where ["map_layer" is not "NULL_VALUE" and] "column_1" is greater than "column_2"

Note that you will need to fill in "<NULL_VALUE>" with the actual value that you get returned (e.g. "" for an empty string);