Function diff_statements 

pub fn diff_statements(
    table: &str,
    dim_cols: &[String],
    vt: ValueType,
    old: &ResultRows,
    new: &ResultRows,
) -> Result<Vec<Statement>>

The statements that turn old (the table’s rows) into new (the engine’s rows) of a vt measure: at most one batched upsert of new/changed rows and one batched delete of vanished rows. Unchanged rows (bit-identical value) are skipped; a value that is not a vt is an error. With no dimension columns (a dimensionless measure’s one-row table) the upsert replaces the table’s row and the delete empties it.