How to pick a default value to the column in the trigger?

We implement some triggers which perform some operations with insert dat开发者_如何学Goa before committing them to the database and when some conditions fail the trigger should pick up the default value for corresponding column.

How to perform it inside the trigger?

Thank you. PS. we work with PostgreSQL, but implementations with other DBMS may give a hint.

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NEW.colname = DEFAULT will do the trick.