Function execute 

pub async fn execute<S: StorageBackend>(
    storage: &S,
    stmt: &Statement,
    parameters: &[AttributeValue],
    limit: Option<usize>,
) -> Result<Option<Vec<Item>>>

Execute a parsed PartiQL statement.

Returns Some(items) for SELECT (may be empty) and for a DELETE or UPDATE carrying a RETURNING clause (the deleted item or the requested projection); None for a write with no RETURNING clause. An optional limit bounds how many rows a SELECT evaluates (reads), not how many it returns, matching DynamoDB’s Limit and the Query/Scan semantics.