数据仓库服务 GAUSSDB(DWS)-聚合函数:hll_add_agg(hll_hashval, int32 log2m, int32 regwidth, int64 expthresh, int32 sparseon)

时间:2024-04-18 16:25:15

hll_add_agg(hll_hashval, int32 log2m, int32 regwidth, int64 expthresh, int32 sparseon)

描述:把哈希后的数据按照分组放到hll中, 依次制定参数log2m、regwidth、expthresh、sparseon。sparseon取值范围为0或者1。

返回值类型:hll

示例:

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 SELECT hll_cardinality(hll_add_agg(hll_hash_text(c), NULL, 1, 4, 0)) FROM t_data;
 hll_cardinality  
------------------
 496.628982624022
(1 row)
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