Don't update column if update value is null

Drop the SELECT statement, there is no need for, just use the current value:

UPDATE some_table SET  column_1 = COALESCE(param_1, column_1),  column_2 = COALESCE(param_2, column_2),  column_3 = COALESCE(param_3, column_3),  column_4 = COALESCE(param_4, column_4),  column_5 = COALESCE(param_5, column_5)WHERE id = some_id;

Neat trick, thanks Przemek, Frank & Erwin!

I suggest a minor edit to Erwin's answer to avoid empty updates. If any parameters were null (meaning: "use the old value"), the row was updated each time even though the row values did not change (after the first update).

By adding "param_x IS NOT NULL", we avoid empty updates:

UPDATE some_table SET    column_1 = COALESCE(param_1, column_1),    column_2 = COALESCE(param_2, column_2),    ...WHERE id = some_idAND  (param_1 IS NOT NULL AND param_1 IS DISTINCT FROM column_1 OR      param_2 IS NOT NULL AND param_2 IS DISTINCT FROM column_2 OR     ... );

Additionally, to avoid empty updates:

UPDATE some_table SET  column_1 = COALESCE(param_1, column_1),  column_2 = COALESCE(param_2, column_2)  ...WHERE id = some_id;AND  (param_1 IS DISTINCT FROM column_1 OR      param_2 IS DISTINCT FROM column_2 OR      ...     );

This assumes target columns to be defined NOT NULL. Else, see Geir's extended version.