code year
code
year
number
text number
a 1927
list each code not associated to a year .
NN DT NN RB VBN TO DT NN .
CH1|CH2|LL1|LL2
Keyword Column Keyword Keyword Keyword Column Keyword Keyword
select c1 from w where c2_number is null
None None Column Keyword Keyword Keyword None Column None
c1 ['null', 'null_null'] ['null', 'null_null'] ['null', 'null_null'] c2_number