Secondo il codice sorgente che si trova qui, a partire dalla riga 850, PostgreSQL non limita esplicitamente il numero di argomenti.
Quello che segue è un commento al codice dalla riga 870:
/*
* We try to generate a ScalarArrayOpExpr from IN/NOT IN, but this is only
* possible if the inputs are all scalars (no RowExprs) and there is a
* suitable array type available. If not, we fall back to a boolean
* condition tree with multiple copies of the lefthand expression.
* Also, any IN-list items that contain Vars are handled as separate
* boolean conditions, because that gives the planner more scope for
* optimization on such clauses.
*
* First step: transform all the inputs, and detect whether any are
* RowExprs or contain Vars.
*/
