SQL adds two columns of int data from the same table, and some of the data is empty

You can't add that!

Some data is null, null+ any value =null

Not if you say that.

Update Set HY_MYGGCYSWCQKB. Sj_by_sr=hy_myggcyswcqkb. Sj_by_sr+hy_myggcyswcqkb. Sj_by_sr_tz-hy_myggcyswcqkb. SJ_BY_SR_TJ;

If there is a column that is not NULL, the result of the addition is null.

Normal, yes.

SELECT
  Total + Money  
From
  Table

You can do it.
But:
Some of the data is empty and needs to be  based on different databases,  with unused functions
That  is, if the data is empty, then it is  calculated according to 0
Oracle  or  DB2  using    NVL (total, 0)  +   NVL (Money, 0)
SQL  Server uses  ISNULL (total, 0)  +   ISNULL (Money, 0)
MySQL  or SQLite    use Ifnull (total, 0)  +  ifnull (Money, 0)

SQL adds two columns of int data from the same table, and some of the data is empty