HLL_CARDINALITY(hll)
HLL_CARDINALITY is used to calculate the cardinality of a single HLL type value.
MySQL > select HLL_CARDINALITY(uv_set) from test_uv; +---------------------------+ | hll_cardinality(`uv_set`) | +---------------------------+ | 3 | +---------------------------+
HLL,HLL_CARDINALITY