Built-in Functions

HLL has a series of built-in functions for internal data processing. Generally, users do not need to know how to use these functions. For details, see Table 1 Built-in functions.

**Table 1** Built-in functions
Function	Description
hll_in	Receives HLL data in string format.
hll_out	Sends HLL data in string format.
hll_recv	Receives HLL data in bytea format.
hll_send	Sends HLL data in bytea format.
hll_trans_in	Receives hll_trans_type data in string format.
hll_trans_out	Sends hll_trans_type data in string format.
hll_trans_recv	Receives hll_trans_type data in bytea format.
hll_trans_send	Sends hll_trans_type data in bytea format.
hll_typmod_in	Receives typmod data.
hll_typmod_out	Sends typmod data.
hll_hashval_in	Receives hll_hashval data.
hll_hashval_out	Sends hll_hashval data.
hll_add_trans0	Works similar to hll_add. No input parameter is specified during initialization. It is usually used in the first phase of DNs in distributed aggregation operations.
hll_add_trans1	Works similar to hll_add. An input parameter is specified during initialization. It is usually used in the first phase of DNs in distributed aggregation operations.
hll_add_trans2	Works similar to hll_add. Two input parameters are specified during initialization. It is usually used in the first phase of DNs in distributed aggregation operations.
hll_add_trans3	Works similar to hll_add. Three input parameters are specified during initialization. It is usually used in the first phase of DNs in distributed aggregation operations.
hll_add_trans4	Works similar to hll_add. Four input parameters are specified during initialization. It is usually used in the first phase of DNs in distributed aggregation operations.
hll_union_trans	Works similar to hll_union and is used on the first phase of DNs in distributed aggregation operations.
hll_union_collect	Works similar to hll_union and is used on the second phase of CNs in distributed aggregation operations to summarize the results of each DN.
hll_pack	Is used on the third phase of CNs in distributed aggregation operations to convert a user-defined type hll_trans_type to the HLL type.
hll	Converts an HLL type to another HLL type. Input parameters can be specified.
hll_hashval	Converts the bigint type to the hll_hashval type.
hll_hashval_int4	Converts the int4 type to the hll_hashval type.