Function column_default_sql 

pub fn column_default_sql(
    pyql: &str,
    schema: &SchemaDescriptor,
) -> Option<String>

The SQL for a pointer’s PyQL default as a column DEFAULT clause, or None when a column DEFAULT cannot hold it — it reads a session global, selects an object, or otherwise needs the query around it. Those are applied by compile_insert instead; see inlined_pointer_defaults.