hello,

ok, to me "a column" could have 5, 10, 15, etc ... rows. Anyway,

If you want to update a column value to null through query
 UPDATE YourTable SET myColumn = null --this will update every myColumn to null in YourTable

if you want to update a single cell in the column to null from the table
  Click on the cell and use Ctrl + 0

Hello
Run the update command for set null values. suppose column name is Country and tablename is UserCountry, then command will be as follows:
UPDATE UserCountry SET Country = NULL

Use the NULL keyword to update
update tablename set column1=null where id=1

i have to update a column to the NULL

Hi,
When you create column for a table, check Allow Null column to true.