Language reference
Log (logarithm)
Syntax
Log(<number>)
Log(<base>, <number>)
π Log(value) → log_value (Measurements)Description
Log returns the natural logarithm (base e) of a number, or with two arguments the logarithm of the second to the base given first: Log(2, 8) is 3. It is used to compress wide-ranging values onto a smaller scale and in growth/decay and statistical calculations.
Technical Description
Log(x: NUMBER) → NUMBER. Returns ln(x) (Math.log). The argument must be positive (else an evaluation error). NULL input returns NULL. PURE, DETERMINISTIC. Floating-point result.
Log(b: NUMBER, y: NUMBER) → NUMBER. Returns log_b(y) = ln(y) / ln(b), in SQL's argument order (PostgreSQL's LOG(b, x)), and exactly the integer n where y is b to the n: Log(10, 1000) is 3, not 2.9999999999999996. Both arguments must be positive and the base must not be 1, else an evaluation error. A NULL in either returns NULL.
Examples
Log-transform a measurement:
π Log(value) → log_value (Measurements)PROJECT Log(value) -> log_value (Measurements)Filter on a log-scaled threshold:
σ Log(amount) > 10 (Transactions)SELECT Log(amount) > 10 (Transactions)Bits needed to count to n:
π Ceil(Log(2, n)) → bits (Counters)PROJECT Ceil(Log(2, n)) -> bits (Counters)Limitations
Errors on a non-positive argument (x ≤ 0), and on a base of 1. NUMBER only; NULL in → NULL out. With one argument this is the natural log (base e), where SQL's one-argument LOG(x) is base 10 in PostgreSQL: write Log10(x) for that.
Alternatives
Exp is the inverse (e^x). Log10(x) is the base-10 logarithm.
SQL names
LN is the one-argument form by SQL's name: LN(x) is Log(x). LOG itself is the natural logarithm, as in MySQL and SQL Server; PostgreSQL's one-argument log is base 10, which here is Log10.