Update with results of another sql

Question

With the sql below I count how many records I have in tableB for each code. The total field is assigned the result of the count and the code the code field of the record.

SELECT
    "count" (*) as total,
    tableB."code" as code
FROM
    tableB 
WHERE
    tableB.code LIKE '%1'
GROUP BY
    tableB.code

In tableA I have a sequence field and I update with the result of total (obtained in the previous sql) plus 1 Do this for each code. I tried this and it did not work, can someone help me?

UPDATE tableA
SET tableA.sequence = (tableB.total + 1) where tableA."code" = tableB.code
FROM
    (
        SELECT
            "count" (*) as total,
            tableB."code" as code
        FROM
            tableB 
        WHERE
            tableB.code LIKE '%1'
        GROUP BY
            tableB.code
    )

I edited for my tables are as mostar believe facillita understanding of my need

tableA

code  sequence
100      null
200      null


table B

code  sequence
100      1
100      2
100      3
100      4
......
100      17
200      1
200      2
200      3
200      4
......
200      23

Need to update the sequence blank field in tableA with the number 18 to code = 100
Need to update the sequence blank field in tableA with the number 24 to code = 200

Answer 1

This assumes that code is unique in table_a:

with max_seq as (
   select code,
          max(sequence) + 1 as max_seq
   from table_b
   group by code
) 
update table_a
  set sequence = ms.max_seq
from max_seq ms
where table_a.code = ms.code;

SQLFiddle example: http://sqlfiddle.com/#!15/745a7/1