PostgreSQL获取汉字拼音首字母函数

本文转自http://blog.qdac.cc/?p=1281

--© 2014,swish，原版首发：http://blog.qdac.cc/?p=1281，自由使用，保留版权
CREATE OR REPLACE FUNCTION CnFirstChar(s character varying)
  RETURNS character varying AS
$BODY$
declare
  retval character varying;
  c character varying;
  l integer;
  b bytea;  
  w integer;
begin
l=length(s);
retval='';
while l>0 loop
  c=left(s,1);
  b=convert_to(c,'GB18030')::bytea;
  if get_byte(b,0)<127 then
    retval=retval || upper(c);
  elsif length(b)=2 then
    begin
    w=get_byte(b,0)*256+get_byte(b,1);
    --汉字GBK编码按拼音排序，按字符数来查找，基于概率来说，效率应该比挨个强:)
    if w between 48119 and 49061 then --"J";48119;49061;942
      retval=retval || 'J';
    elsif w between 54481 and 55289 then --"Z";54481;55289;808
      retval=retval || 'Z';
    elsif w between 53689 and 54480 then --"Y";53689;54480;791
      retval=retval || 'Y';
    elsif w between 51446 and 52208 then --"S";51446;52208;762
      retval=retval || 'S';
    elsif w between 52980 and 53640 then --"X";52980;53640;660
      retval=retval || 'X';
    elsif w between 49324 and 49895 then --"L";49324;49895;571
      retval=retval || 'L';
    elsif w between 45761 and 46317 then --"C";45761;46317;556
      retval=retval || 'C';
    elsif w between 45253 and 45760 then --"B";45253;45760;507
      retval=retval || 'B';
    elsif w between 46318 and 46825 then --"D";46318;46825;507
      retval=retval || 'D';
    elsif w between 47614 and 48118 then --"H";47614;48118;504
      retval=retval || 'H';
    elsif w between 50906 and 51386 then --"Q";50906;51386;480
      retval=retval || 'Q';
    elsif w between 52218 and 52697 then --"T";52218;52697;479
      retval=retval || 'T';
    elsif w between 49896 and 50370 then --"M";49896;50370;474
      retval=retval || 'M';
    elsif w between 47297 and 47613 then --"G";47297;47613;316
      retval=retval || 'G';
    elsif w between 47010 and 47296 then--"F";47010;47296;286
      retval=retval || 'F';
    elsif w between 50622 and 50905 then--"P";50622;50905;283
      retval=retval || 'P';
    elsif w between 52698 and 52979 then--"W";52698;52979;281
      retval=retval || 'W';
    elsif w between 49062 and 49323 then--"K";49062;49323;261
      retval=retval || 'K';
    elsif w between 50371 and 50613 then --"N";50371;50613;242
      retval=retval || 'N';
    elsif w between 46826 and 47009 then--"E";46826;47009;183
      retval=retval || 'E';
    elsif w between 51387 and 51445 then--"R";51387;51445;58
      retval=retval || 'R';
    elsif w between 45217 and 45252 then --"A";45217;45252;35
      retval=retval || 'A';
    elsif w between 50614 and 50621 then --"O";50614;50621;7
      retval=retval || 'O';
    end if;
    end;
  end if;
  s=substring(s,2,l-1);
  l=l-1;
end loop;
return retval;
end;
$BODY$
  LANGUAGE plpgsql IMMUTABLE;