here is a hack using parsename

SELECT PARSENAME(REPLACE('120/20','/','.'),2) as SP, 
PARSENAME(REPLACE('120/20','/','.'),1) as DP

Output

SP DP
120 20

You can use ALTER to do that.

Example:

ALTER TABLE table_name
ADD column_name data_type

You can try to create computed columns in case you are not allowed or able to populate the columns on write/update:

CREATE TABLE DataSource 
(
    ID INT PRIMARY KEY
   ,BPValue VARCHAR(12)
)

GO

INSERT INTO DataSource (ID, BPValue)
VALUES (1, '123/98')
      ,(2, '118/72')
      ,(3, '97/74');

GO

ALTER TABLE DataSource
ADD Value1 AS TRY_CAST(SUBSTRING(BPValue, 0, CHARINDEX('/', BPValue)) AS INT)

ALTER TABLE DataSource
ADD Value2 AS TRY_CAST(SUBSTRING(BPValue, CHARINDEX('/', BPValue) + 1, 128) AS INT)

GO

SELECT *
FROM DataSource

Also, the columns can be materialized if you create them with the PERSISTED option. Otherwise, the computation is perform on read, which can be slow on certain cases.

The better way, is to create two separate columns and populate the data on insert/update.

The above can be done on MySQL , too. Here is the link to the official documentation.