关于postgresql运算符计算问题

你的例子中用到了>>,^,&操作符，这些操作符对应的操作数类型如下：

postgres=# \do+ >>
                                           List of operators
   Schema   | Name | Left arg type | Right arg type | Result type |   Function    |     Description     
------------+------+---------------+----------------+-------------+---------------+---------------------
 pg_catalog | >>   | anyrange      | anyrange       | boolean     | range_after   | is right of
 pg_catalog | >>   | bigint        | integer        | bigint      | int8shr       | bitwise shift right
 pg_catalog | >>   | bit           | integer        | bit         | bitshiftright | bitwise shift right
 pg_catalog | >>   | box           | box            | boolean     | box_right     | is right of
 pg_catalog | >>   | circle        | circle         | boolean     | circle_right  | is right of
 pg_catalog | >>   | inet          | inet           | boolean     | network_sup   | is supernet
 pg_catalog | >>   | integer       | integer        | integer     | int4shr       | bitwise shift right
 pg_catalog | >>   | point         | point          | boolean     | point_right   | is right of
 pg_catalog | >>   | polygon       | polygon        | boolean     | poly_right    | is right of
 pg_catalog | >>   | smallint      | integer        | smallint    | int2shr       | bitwise shift right
(10 rows)

postgres=# \do+ &
                                      List of operators
   Schema   | Name | Left arg type | Right arg type | Result type |  Function   | Description 
------------+------+---------------+----------------+-------------+-------------+-------------
 pg_catalog | &    | bigint        | bigint         | bigint      | int8and     | bitwise and
 pg_catalog | &    | bit           | bit            | bit         | bitand      | bitwise and
 pg_catalog | &    | inet          | inet           | inet        | inetand     | bitwise and
 pg_catalog | &    | integer       | integer        | integer     | int4and     | bitwise and
 pg_catalog | &    | macaddr       | macaddr        | macaddr     | macaddr_and | bitwise and
 pg_catalog | &    | smallint      | smallint       | smallint    | int2and     | bitwise and
(6 rows)

postgres=# \do+ ^
                                              List of operators
   Schema   | Name |  Left arg type   |  Right arg type  |   Result type    |   Function    |  Description   
------------+------+------------------+------------------+------------------+---------------+----------------
 pg_catalog | ^    | double precision | double precision | double precision | dpow          | exponentiation
 pg_catalog | ^    | numeric          | numeric          | numeric          | numeric_power | exponentiation
(2 rows)

postgres=# select ((2)^(-86)) & 0xFF;
ERROR:  operator does not exist: double precision & integer
LINE 1: select ((2)^(-86)) & 0xFF;
                           ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.

报错的是&这个操作符，因为^产生了numeric的结果，所以需要转成&支持的类型才行。
解决办法，转换成int8：

postgres=# select ((2)^(-86))::int8 & 0xFF;
 xff 
-----
   0
(1 row)

如果要实现JAVA程序一样的效果，需要修改一下写法，^在PG里是pow，不是亦或。亦或是#符号。

postgres=# select ((0) # (-86))::int4 & 255;
 ?column? 
----------
      170
(1 row)

今天在遇到同类问题： date类型数据 减去 （默认精度）numeric数据类型。一直提示：Error：operator does not exists :date - numeric。
显示转换 ：：integer，解决。 多谢。

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