constcol [-noparam] [-acceptnull] [-[no]parallel] [<colid-list>]
Identifies columns with constant values. Such columns are removed from the table and by default their fixed value is added to the table as a table parameter with the same name as the removed column. Such columns may have scalar or array values.
controls whether constant columns identified are recorded instead
as table parameters (per-table metadata items).
By default they are, but supplying
means these values will just be discarded.
controls how blank values in candidate columns are treated.
By default, all values in a column must be strictly the same
for a column to be identified as constant value,
-acceptnull is supplied
then a column will be treated as constant if all its entries
are either a single fixed value or blank.
controls whether processing is done using multithreading
for large tables.
gives the columns to be assessed by this filter;
if not supplied, all columns will be examined.
Syntax for the
<colid-list> argument is described in Section 6.3.