Function validate_mutation_targets 

pub fn validate_mutation_targets<'a, E: 'a>(
    catalog: &dyn AssignmentColumnCatalog,
    table: &str,
    targets: impl IntoIterator<Item = &'a AssignmentTarget<E>>,
    action: &str,
    insert: bool,
) -> Result<(), SQLError>

Validate partial targets without rejecting independent writes into the same column.