Question

此功能是一种解决方法……没有什么比更好的性能更好？

CREATE or REPLACE FUNCTION varbit_to_int(v varbit) RETURNS int AS $f$
  SELECT CASE bit_length(v)
    WHEN 1 THEN v::bit(1)::int
    WHEN 2 THEN v::bit(2)::int
    WHEN 3 THEN v::bit(3)::int
    ...
    WHEN 30 THEN v::bit(30)::int
    WHEN 31 THEN v::bit(31)::int
    WHEN 32 THEN v::bit(32)::int
    ELSE NULL::int
  END
$f$ LANGUAGE SQL IMMUTABLE;

bigint的相同问题：

CREATE or replace FUNCTION varbit_to_bigint(p varbit) RETURNS bigint AS $f$
  SELECT CASE bit_length($1)
    WHEN 1 THEN $1::bit(1)::bigint
    WHEN 2 THEN $1::bit(2)::bigint
    WHEN 3 THEN $1::bit(3)::bigint
    ...
    WHEN 62 THEN $1::bit(62)::bigint
    WHEN 63 THEN $1::bit(63)::bigint
    WHEN 64 THEN $1::bit(64)::bigint
    ELSE NULL::bigint
  END
$f$ LANGUAGE SQL IMMUTABLE STRICT;

在循环中多次使用似乎浪费CPU资源，只是为了避免“无法将类型位转换为整数”错误。也许外部的C语言库可以执行此操作以及其他有用的转换。

注意 select b'101'::bit(64)::bigint != b'101'::bigint;

Answer 1

我测试了几个具有内置功能的变体（仅适用于bigint），在我对Postgres 11的本地测试中，该变体与OVERLAY()的测试结果最快：

CREATE OR REPLACE FUNCTION varbit2bigint2(b varbit)
  RETURNS bigint AS
$func$
SELECT OVERLAY(bit(64) '0' PLACING b FROM 65 - bit_length(b))::bigint
$func$  LANGUAGE SQL IMMUTABLE;

其他候选人：

请注意，空位字符串（''）到0与NULL的转换不同。适应您的需求！

您的功能：

CREATE OR REPLACE FUNCTION varbit2bigint1(b varbit)
  RETURNS bigint AS
$func$
  SELECT CASE bit_length($1)
   WHEN  1 THEN $1::bit(1)::bigint
   WHEN  2 THEN $1::bit(2)::bigint
   WHEN  3 THEN $1::bit(3)::bigint
   WHEN  4 THEN $1::bit(4)::bigint
   WHEN  5 THEN $1::bit(5)::bigint
   WHEN  6 THEN $1::bit(6)::bigint
   WHEN  7 THEN $1::bit(7)::bigint
   WHEN  8 THEN $1::bit(8)::bigint
   WHEN  9 THEN $1::bit(9)::bigint
   WHEN 10 THEN $1::bit(10)::bigint
   WHEN 11 THEN $1::bit(11)::bigint
   WHEN 12 THEN $1::bit(12)::bigint
   WHEN 13 THEN $1::bit(13)::bigint
   WHEN 14 THEN $1::bit(14)::bigint
   WHEN 15 THEN $1::bit(15)::bigint
   WHEN 16 THEN $1::bit(16)::bigint
   WHEN 17 THEN $1::bit(17)::bigint
   WHEN 18 THEN $1::bit(18)::bigint
   WHEN 19 THEN $1::bit(19)::bigint
   WHEN 20 THEN $1::bit(20)::bigint
   WHEN 21 THEN $1::bit(21)::bigint
   WHEN 22 THEN $1::bit(22)::bigint
   WHEN 23 THEN $1::bit(23)::bigint
   WHEN 24 THEN $1::bit(24)::bigint
   WHEN 25 THEN $1::bit(25)::bigint
   WHEN 26 THEN $1::bit(26)::bigint
   WHEN 27 THEN $1::bit(27)::bigint
   WHEN 28 THEN $1::bit(28)::bigint
   WHEN 29 THEN $1::bit(29)::bigint
   WHEN 30 THEN $1::bit(30)::bigint
   WHEN 31 THEN $1::bit(31)::bigint
   WHEN 32 THEN $1::bit(32)::bigint
   WHEN 33 THEN $1::bit(33)::bigint
   WHEN 34 THEN $1::bit(34)::bigint
   WHEN 35 THEN $1::bit(35)::bigint
   WHEN 36 THEN $1::bit(36)::bigint
   WHEN 37 THEN $1::bit(37)::bigint
   WHEN 38 THEN $1::bit(38)::bigint
   WHEN 39 THEN $1::bit(39)::bigint
   WHEN 40 THEN $1::bit(40)::bigint
   WHEN 41 THEN $1::bit(41)::bigint
   WHEN 42 THEN $1::bit(42)::bigint
   WHEN 43 THEN $1::bit(43)::bigint
   WHEN 44 THEN $1::bit(44)::bigint
   WHEN 45 THEN $1::bit(45)::bigint
   WHEN 46 THEN $1::bit(46)::bigint
   WHEN 47 THEN $1::bit(47)::bigint
   WHEN 48 THEN $1::bit(48)::bigint
   WHEN 49 THEN $1::bit(49)::bigint
   WHEN 50 THEN $1::bit(50)::bigint
   WHEN 51 THEN $1::bit(51)::bigint
   WHEN 52 THEN $1::bit(52)::bigint
   WHEN 53 THEN $1::bit(53)::bigint
   WHEN 54 THEN $1::bit(54)::bigint
   WHEN 55 THEN $1::bit(55)::bigint
   WHEN 56 THEN $1::bit(56)::bigint
   WHEN 57 THEN $1::bit(57)::bigint
   WHEN 58 THEN $1::bit(58)::bigint
   WHEN 59 THEN $1::bit(59)::bigint
   WHEN 60 THEN $1::bit(60)::bigint
   WHEN 61 THEN $1::bit(61)::bigint
   WHEN 62 THEN $1::bit(62)::bigint
   WHEN 63 THEN $1::bit(63)::bigint
   WHEN 64 THEN $1::bit(64)::bigint
   ELSE NULL::bigint
  END
$func$  LANGUAGE SQL IMMUTABLE;  -- no STRICT modifier

用'0'左填充文本表示形式

CREATE OR REPLACE FUNCTION pg_temp.varbit2bigint3(b varbit)
  RETURNS bigint AS
$func$
SELECT lpad(b::text, 64, '0')::bit(64)::bigint
$func$  LANGUAGE SQL IMMUTABLE;

在转换前进行位移：

CREATE OR REPLACE FUNCTION varbit2bigint4(b varbit)
  RETURNS bigint AS
$func$
SELECT (bit(64) '0' || b << bit_length(b))::bit(64)::bigint
$func$  LANGUAGE SQL IMMUTABLE;

db <>提琴here

您的反馈

这不是最坏的情况，它更快！

EXPLAIN ANALYZE select 
  varbit_to_bigint(osm_id::bit(64)::varbit) 
from planet_osm_point limit 10000 ;
-- Planning time: 0.697 ms
-- Execution time: 1133.571 ms

EXPLAIN ANALYZE select 
  lpad(osm_id::bit(64)::varbit::text, 32, '0')::bit(64)::bigint 
from planet_osm_point limit 10000;
-- Planning time: 0.105 ms
-- Execution time: 26.429 ms

您将在问题中显示带有该功能的STRICT变体的 bigint 修饰符（不确定为什么与integer变体不同）。如果那代表您实际测试的功能，则我希望观察到的大多数性能差异是由于添加了 {STRICT 修饰符，从而防止了功能内联。 Quoting the Postgres Wiki:

如果函数被声明为STRICT，那么计划者必须能够证明主体表达式必须返回NULL（如果有）参数为null。目前，只有在以下情况下才能满足此条件：每个参数至少被引用一次，并且所有功能，主体中使用的运算符和其他构造本身就是STRICT。

这似乎严重损害了您的功能-而我的获胜者似乎并不受影响，其他两个变体的速度甚至快了10％。与STRICT函数相同的提琴手：

db <>提琴here

将varbit转换为int的其他方法？还有bigint？

1 个答案:

其他候选人：

您的反馈