Function prune_filter 

pub fn prune_filter(expr: &Expr, table: &Schema) -> Result<Option<Expr>>

A filter for a scan of table with the rows that can match expr. None means that every row is kept. crate::NdScanner::filter_expr uses it.

expr uses the Lance table columns, for example get_field(col("sst"), "values"), get_field(col("sst"), "attrs") or get_field(col("__global_attrs__"), "id"). lance-nd does not check or change the names, so Lance reports a wrong name in the scan.

A value part reads <variable>.values. It changes into a filter on the stats column. The changed part keeps every row that can match, and skips a row only when the stats show that no value of the row matches. A value part without a stats form keeps every row.

Each other part, for example on attributes, is exact for a row, so it stays as it is. These rules apply:

• AND: a side without a stats form goes away, so more rows are kept.
• OR: both sides need a form, or the full OR keeps every row.
• NOT: only over parts without values. Over a value part, it keeps every row.