使用指南SQL 手册SQL 函数HLL 函数HLL_EMPTY本页总览HLL_EMPTYHLL_EMPTY description Syntax HLL_EMPTY(value) HLL_EMPTY 返回一个 hll 类型的空值。 example MySQL > select hll_cardinality(hll_empty());+------------------------------+| hll_cardinality(hll_empty()) |+------------------------------+| 0 |+------------------------------+ keywords HLL,HLL_EMPTY