update column based on values in another (SAS, SQL)

I have a table with 2 columns, I need to update one of them based on values in another.

Column A is a flag (1s and 0s), column B is a string column. I need update column B based on the flag in column A. If A = 1 then column B needs to preserve its values, if column A is 0, I need to set column B to blank.

column A.    Column B.      
1            abc         <-keep
0            abc         <-set to blank
1            abc         <-keep


PROC SQL;
update table abc
set column B = 
case when A.column IS NOT NULL then A.column = A.column
else A.column = ' '
end  

>Solution :

Simply using Update with CASE statement to do what you want:

update column B based on the flag in column A. If A = 1 then column B
needs to preserve its values, if column A is 0, I need to set column B
to blank.

UPDATE
  your_table
SET
  column_B = CASE
            WHEN column_A = 1 THEN column_B -- columnB needs to preserve its value
            ELSE ''  -- set column B to blank.
  END;

Before:

column_A    column_B
1           abc
0           abc
1           abc

After update:

column_A    column_B
1           abc
0           
1           abc

dbfiddle DEMO