openGauss SQL参考—函数和操作符：HLL函数和操作符（7）

操作符

• =

  描述：比较hll或hll_hashval的值是否相等。

  返回值类型：bool

  示例：

  --hll
  openGauss=# select (hll_empty() || hll_hash_integer(1)) = (hll_empty() || hll_hash_integer(1));
  column 
  ----------
   t
  (1 row)
  
  --hll_hashval
  openGauss=# select hll_hash_integer(1) = hll_hash_integer(1);
   ?column? 
  ----------
   t
  (1 row)
  

• <> or !=

  描述：比较hll或hll_hashval是否不相等。

  返回值类型：bool

  示例：

  --hll
  openGauss=# select (hll_empty() || hll_hash_integer(1)) <> (hll_empty() || hll_hash_integer(2));
   ?column? 
  ----------
   t
  (1 row)
  
  --hll_hashval
  openGauss=# select hll_hash_integer(1) <> hll_hash_integer(2);
   ?column? 
  ----------
   t
  (1 row)
  

• ||

  描述：可代表hll_add、hll_union、hll_add_rev三个函数的功能。

  返回值类型：hll

  示例：

  --hll_add
  openGauss=# select hll_empty() || hll_hash_integer(1);
                                    ?column?
  ----------------------------------------------------------------------------
   \x484c4c08000002002b0900000000000000f03f3e2921ff133fbaed3e2921ff133fbaed00
  (1 row)
  
  --hll_add_rev
  openGauss=# select hll_hash_integer(1) || hll_empty();
                                    ?column?
  ----------------------------------------------------------------------------
   \x484c4c08000002002b0900000000000000f03f3e2921ff133fbaed3e2921ff133fbaed00
  (1 row)
  
  --hll_union
  openGauss=# select (hll_empty() || hll_hash_integer(1)) || (hll_empty() || hll_hash_integer(2));
                                            ?column?
  --------------------------------------------------------------------------------------------
   \x484c4c10002000002b090000000000000000400000000000000000b3ccc49320cca1ae3e2921ff133fbaed00
  (1 row)
  

• #

  描述：计算出hll的Dintinct值, 同hll_cardinality函数。

  返回值类型：int

  示例：

  openGauss=# select #(hll_empty() || hll_hash_integer(1));
   ?column? 
  ----------
          1
  (1 row)