[deredede]

While sub-optimal, your first example is probably fine to send and I'd expect to be simplified early during query planning at a negligible cost to the database server.

What you shouldn't send is queries like:

    SELECT \* FROM users
    WHERE ($1 IS NULL OR id = $1)
        AND ($2 IS NULL OR username = $2)
        AND ($3 IS NULL OR age > $3)
        AND ($4 IS NULL OR age < $4)

because now the database (probably) doesn't know the value of the parameters during planning and needs to consider all possibilities.

[oever]

Interesting. I try to use prepared statements to avoid redoing the planning. But since the database schema is small compared to the data, the cost of query planning is quickly negligible compared to running an generic query that is inefficient.