Column name, as it appears in reader.header.info.columns. An unknown
name, or a known one the writer did not index, throws
AttributeIndexNotFound: this reader queries indices, it never falls back
to a scan. Json and Binary columns throw UnsupportedColumnType.
Compared against the column's values. The admissible JS type follows the
column's ColumnType: number (integral) for the integer types,
number for Float/Double, boolean for Bool, string for
String, bigint or an integral number for Long/ULong, and either
a DateTimeKey or a Date for DateTime -- a Date is widened
losslessly, but only a DateTimeKey can express sub-millisecond
precision. Anything else throws InvalidArgument before any I/O.
One attribute predicate.
valueisunknownbecause the admissible type depends on the column's declared type, which is only known once the header has been read.