问题
How does substring work on hexadecimal values?
See this:
PRINT SUBSTRING(0x6,1,1)
PRINT SUBSTRING(0xF6,1,1)
PRINT SUBSTRING(0xFF6,1,1)
PRINT SUBSTRING(0xFFF6,1,1)
...outputs...
0x06
0xF6
0x0F
0xFF
...which currently looks as a complete nonsense to me. But it can somehow used in detecting which column is updated in trigger (see COLUMNS_UPDATED()).
I tried:
- intermediately converted it to string and then substring it
- intermediately converted it to int, then string and then substring it
- searching in MSDN substring() documentation
- googling
Can someone explain how is that conversion done?
回答1:
The SUBSTRING documentation isn't particularly clear about how it treats binary values, referring to 'characters' rather than bytes. But it's effectively treating the input as a byte sequence, and with 1, 1 you are asking for the first byte of the sequence:
Input Byte sequence
----------------------
0x6 06
0xF6 F6
0xFF6 0F F6
0xFFF6 FF F6
Output of SUBSTRING(input, 1, 1) :
0x06
0xF6
0x0F
0xFF
来源：https://stackoverflow.com/questions/18098798/substring-and-hex-value