当前项目中用到了elfhash函数算出HASH值后再进行分表，
当需要在MYSQL里进行查询时比较麻烦，需要先算出HASH值才能确定用户数据被分到哪个表里，
于是把这个函数用SQL写成函数，方便使用。
CREATE DEFINER=`test`@`127.0.0.1` FUNCTION `elfhash`(strkey varchar(256)) RETURNS int(11)
NO SQL
BEGIN
#Routine body goes here...
/*
unsigned long ELFHash(const char *key)
{
unsigned long h = 0;
unsigned long x = 0;
while (*key)
{
h = (h << 4) + (*key++);
if ((x = h & 0xF0000000L) != 0)
{
h ^= (x >> 24);
h &= ~x;
}
}
return (h & 0x7FFFFFFF);
}
*/
DECLARE h INT UNSIGNED DEFAULT 0;
DECLARE x INT UNSIGNED DEFAULT 0;
DECLARE k INT UNSIGNED DEFAULT 0;
DECLARE strLen INT UNSIGNED DEFAULT 0;
DECLARE pos INT UNSIGNED DEFAULT 0;
SET strLen = LENGTH(strkey)+1;
WHILE (pos<strLen) DO
set k = ASCII(MID(strkey,pos,1));
set h = (h << 4) + k;
SET x = h & 0xF0000000;
IF (x!= 0) THEN
set h = h^(x >> 24);
set h = h&(~x);
END IF;
SET pos = pos +1;
END WHILE;
SET h = h & 0x7FFFFFFF;
RETURN h;
END
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转载请注明：爱开源 » ELFHash SQL实现