Ensure that a column value is supplied in MS SQL Server

Ensure that a column value is supplied in MS SQL Server

 

  

Hi,
Is there something similar to ORACLE before trigger in SQL Server.

Here is what I want to do.

If column A is updated with 'CLOSED', column B needs to be filled with a
non null value. How can I ensure this using a trigger? Column A is
defined with not null and check constraints. Column B has no
constraints whatsoever.
--
Sankar

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