The scalar math functions Client.Local evaluates in SQL expressions, wherever an expression stands (WHERE, the select list, ORDER BY, an aggregate's argument), as InfluxDB 3 does (verified against Core):

• abs(x) — the magnitude, in the argument's type
• round(x), round(x, n) — half away from zero (round(-2.5) is -3.0), to n decimal places (negative n rounds left of the point: round(1234.5678, -2) is 1200.0); always a float, and a zero result keeps the sign of its argument (round(-0.3) is -0.0)
• trunc(x) — toward zero (trunc(-2.75) is -2.0), always a float; a zero it leaves keeps the sign of a fraction (trunc(-0.4) is -0.0) but not of a zero (trunc(-0.0) is 0.0). trunc(x, n) is round(x, n): the engine rounds there (trunc(1234.5678, 2) is 1234.57)
• floor(x), ceil(x) — always a float

An argument that is a decimal (an Int64 with a UInt64) is read as a double, except by abs, which keeps it. An infinity or a NaN is passed on (round(inf) is infinity); round(x, n) that overflows is null on the engine, and here (see InfluxElixir.Client.Local.SQLNumber).

A null argument makes the result null. Names are case-insensitive.

The engine checks the arguments' types when it plans the query, so a wrong one fails the query even when no row would reach the call (check/3). The message depends on where the call stands: in WHERE it carries the type_coercion prefix, in ORDER BY it is cut after its first sentence, and in the select list it has neither. A call in WHERE under a CAST, IS [NOT] NULL, BETWEEN, LIKE, IN or NOT is cut after its first sentence too (:where_cut; see InfluxElixir.Client.Local.SQLPlan for the order the engine reports them in). floor and ceil with a second argument are the engine's 405.