Question

INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)

Now what to check:

If inserted value1 = null, change it to 0

How to do it via trigger? I googled for examples and I have never ever done a trigger, so it is rather confusing.

So far got only this:

CREATE TRIGGER testTrigger
ON myTable
AFTER INSERT, UPDATE, DELETE

Answer 1

You can add default value . This is how it’s done for a new column. For existing one you should add constraint. Check Update 2

ALTER TABLE table_name 
ADD column1 int NOT NULL DEFAULT(0)

Add a column with a default value to an existing table in SQL Server

UPDATE:

To set default value, you should update NULL values at first.

UPDATE table_name 
SET column1 = 0
WHERE column1 IS NULL

UPDATE 2:

Try adding constraint

ALTER TABLE table_name 
ADD CONSTRAINT DF_column1 DEFAULT 0 FOR column1