下面是一个如何做到这一点的例子

A = LOAD 'data.csv' USING PigStorage(',') AS (f1, f2, f3, f4);

B = FOREACH A GENERATE
    ( f1 IS NULL ? 0 : 1 ) AS f1_validity,
    ( f2 IS NULL ? 0 : 1 ) AS f2_validity,
    ( f3 IS NULL ? 0 : 1 ) AS f3_validity,
    ( f4 IS NULL ? 0 : 1 ) AS f4_validity;

C = FOREACH B GENERATE 
    f1_validity + f2_validity + f3_validity + f4_validity AS valid_field_cnt;

我希望我能正确理解你的问题。
我现在也这么做了：）

A = LOAD 'SO/null_data2.csv' USING PigStorage(',') AS (f1, f2, f3, f4);
DESCRIBE A;

--DUMP A;

B = FOREACH A GENERATE
    ( f1 IS NULL ? 0 : 1 ) AS f1_validity,
    ( f2 IS NULL ? 0 : 1 ) AS f2_validity,
        ( f3 IS NULL ? 0 : 1 ) AS f3_validity,
        ( f4 IS NULL ? 0 : 1 ) AS f4_validity,
    ( f1 IS NULL ? 0 : f1 ) AS f1,
    ( f2 IS NULL ? 0 : f2 ) AS f2,
        ( f3 IS NULL ? 0 : f3 ) AS f3,
        ( f4 IS NULL ? 0 : f4 ) AS f4;
DESCRIBE B;

C = FOREACH B GENERATE 
    f1_validity + f2_validity + f3_validity + f4_validity AS not_null_cnt,
    f1 + f2 + f3 + f4 AS sum;
DESCRIBE C;
DUMP C;

A = LOAD 'test8.txt' USING PigStorage('\t') AS (a,b,c,d);
B = FOREACH A GENERATE ( a is null ? 0 : 1 ) AS a1,
                       ( b is null ? 0 : 1 ) AS b1,
                       ( c is null ? 0 : 1 ) AS c1,
                       ( d is null ? 0 : 1 ) AS d1,
                       ( a is null ? 0 : a ) AS a,
                       ( b is null ? 0 : b ) AS b,
                       ( c is null ? 0 : c ) AS c,
                       ( d is null ? 0 : d ) AS d;
C = FOREACH B GENERATE a1 + b1 + c1 + d1 as field_count,
                       ((a + b + c + d) == 0 ? null : (a + b + c + d)) as field_sum;    
DUMP C;

输出