For anyone else who might be interested, this query seems to work:
SHOW SERIES CARDINALITY
More info/ background:
“Series cardinality is the number of unique database, measurement, tag set, and field key combinations in an InfluxDB instance.
For example, assume that an InfluxDB instance has a single database and one measurement. The single measurement has two tag keys: email and status . If there are three different email s, and each email address is associated with two different status es then the series cardinality for the measurement is 6 (3 * 2 = 6)” (InfluxDB glossary | InfluxDB OSS 1.8 Documentation)
