BuildFullDecodeColMap build a map that contains [columnID -> struct{*table.Column, expression.Expression}] from indexed columns and all of its depending columns.

NewRowDecoder returns a new RowDecoder.

RemoveUnusedVirtualCols removes all virtual columns in decodeColMap that cannot found in indexedCols.

SubstituteGenColsInDecodeColMap substitutes generated columns in every expression with non-generated one by looking up decodeColMap.

Column contains the info and generated expr of column.

RowDecoder decodes a byte slice into datums and eval the generated column value.