Oracle 18c

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CREATE TABLE TESTE_NUMBER AS
select '1722. 0000' AS CAMPO1 FROM dual
UNION SELECT '18.123' FROM dual
2 rows affected

SELECT *
FROM TESTE_NUMBER

CAMPO1

1722. 0000

18.123

SELECT SUM(CAST(REPLACE(Campo1, ' ') AS NUMERIC)) AS VOLUME
FROM TESTE_NUMBER

VOLUME

1740

SELECT SUM(CAST(Campo1 AS NUMERIC DEFAULT 0 ON CONVERSION ERROR)) AS VOLUME
FROM TESTE_NUMBER

VOLUME

18.123