如何在varbinary列的第N个字节上执行二进制操作？

Question

我已经能够使用substring(colname, N, 1)字段中获取第N个字节，但是到那时，似乎无法将结果视为二进制了：

> select substring(colname, N, 1) from [...]
\
> select hex(substring(colname, N, 1)) from [...]
5C
> select hex(substring(colname, N, 1) & 0xff) from [...]
0
> select cast(substring(colname, N, 1) as unsigned integer) from [...]
0

相比：

> select cast(0x5c as binary);
\
> select hex(0x5c & 0xff);
5C
> select cast(0x5c as unsigned integer);
92

---

我最终想要得到的是这样的：

> select [...] where substring(colname, N, 1) & 0b00100000 = 0b00100000;

Answer 1

尝试这样的事情：

select ascii(substring(colname,N,1)) from [...]