如何在Sybase SQL Anywhere中模拟MySQL bit_count函数? [英] How to simulate the MySQL bit_count function in Sybase SQL Anywhere?
问题描述
MySQL的bit_count函数在某些情况下非常有用:
MySQL's bit_count function is quite useful for some cases:
http://dev.mysql. com/doc/refman/5.5/en/bit-functions.html#function_bit-count
现在,我想在不支持该功能的其他数据库中使用该功能.最简单的方法是什么(无需创建存储函数,因为我无法在DDL级别上访问客户端数据库).
Now I would like to use that function in other databases, that do not support it. What's the simplest way to do it (without creating a stored function, as I do not have access to the client database on a DDL level).
这是一个非常详细的选项(对于TINYINT
数据类型):
One pretty verbose option is this (for TINYINT
data types):
SELECT (my_field & 1) +
(my_field & 2) >> 1 +
(my_field & 4) >> 2 +
(my_field & 8) >> 3 +
(my_field & 16) >> 4 +
...
(my_field & 128) >> 7
FROM my_table
对于Sybase SQL Anywhere,>>
运算符似乎不可用,因此按2, 4, 8, 16
进行除法也可以.
In the case of Sybase SQL Anywhere, the >>
operator doesn't seem to be available, so a division by 2, 4, 8, 16
works as well.
还有其他更简单的选择吗?
Any other, less verbose options?
推荐答案
我发现这种算法在Java的Integer
和Long
类中略为冗长.不过,我完全不知道为什么它应该以这种方式工作:
I've found this algorithm that's a little less verbose in Java's Integer
and Long
classes. I'm completely oblivious to why it's supposed to work this way, though:
public static int bitCount(int i) {
// HD, Figure 5-2
i = i - ((i >>> 1) & 0x55555555);
i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
i = (i + (i >>> 4)) & 0x0f0f0f0f;
i = i + (i >>> 8);
i = i + (i >>> 16);
return i & 0x3f;
}
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