Null to not null

Question

how make a column from null to not null

Answer 1

You can change the content of the column with the UPDATE statement.
You can change the table definition with the ALTER TABLE statement.
The syntax may vary a bit among different database engines, for example in MySql it would be something like
ALTER TABLE table_name
MODIFY column_name VARCHAR(30) NOT NULL;

If you have data in the table you may have to update all rows first that have null in this column.

Answer 2

table name Customers and column name ph1