Postgres constraint ensuring one column of many is present?

Question

What are good ways to add a constraint to PostgreSQL to check that exactly one column (from a set of columns) contains a non-null value?

Update: It is likely th

Answer 1

Here's a solution using the built-in array functions:

ALTER TABLE your_table
ADD chk_only_one_is_not_null CHECK (array_length(array_remove(ARRAY[col1, col2, col3], NULL), 1) = 1);