Oracle 21c

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ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF';
CREATE TABLE tableA (id PRIMARY KEY, count, filter_condition) AS
  SELECT 1, 10, 'condition' FROM DUAL UNION ALL
  SELECT 2,  5, 'condition' FROM DUAL UNION ALL
  SELECT 3,  1, 'condition' FROM DUAL;
3 rows affected

CREATE TABLE tableB (id, count) AS
  SELECT 1,  5 FROM DUAL UNION ALL
  SELECT 1,  5 FROM DUAL UNION ALL
  SELECT 2,  1 FROM DUAL UNION ALL
  SELECT 2,  3 FROM DUAL;
4 rows affected

MERGE INTO tableA a
USING (
  SELECT id,
         SUM(count) AS total
  FROM   tableb
  GROUP BY id
) b
ON (a.id = b.id AND a.filter_condition = 'condition')
WHEN MATCHED THEN
  UPDATE
  SET a.count = b.total
  WHERE a.count <> b.total;
1 rows affected

SELECT * FROM tableA;


ID
COUNT
FILTER_CONDITION


1
10
condition

2
4
condition

3
1
condition


ROLLBACK;
UPDATE tableA a
SET   count = (SELECT SUM(count) FROM tableB b WHERE b.id = a.id)
WHERE filter_condition = 'condition'
AND   count != (SELECT SUM(count) FROM tableB b WHERE b.id = a.id)
1 rows affected

SELECT * FROM tableA;


ID
COUNT
FILTER_CONDITION


1
10
condition

2
4
condition

3
1
condition