IS NULL不起作用

Question

I have a table like the one above with the two left columns (Both of them are integer) and I added to this table two more fields:

Table1:

Asset_Value    Contract_Value  
-------------------------------
0              NULL             
NULL           200               
0              NULL     

And the query:

Select 
    Asset_Value, Contract_Value,
    Case 
       when Asset_Value is null 
          then 1 
          else 0 
    end As Ind_ForNullA,
    Case 
       when Contract_Value is null
          then 1 
          else 0 
    end As IndForNullC
from 
    table1

However, I get strange results:

Asset_Value Contract_Value  Ind_ForNullA IndForNullC
----------------------------------------------------
0              NULL              1            1
NULL           200               0            0
0              NULL              0            1

Update : Never Mind. Damm comma has been forgetten.

Answer 1

尝试使用''空字符串而不是null。

Answer 2

Why are you bothering to define something as NULL--which is appropriate--but, in this case or that one, changing it to one or zero (an attempt at Boolean, I imagine)--which is inappropriate?

What will you do next: decide that, in a third report, you want to have a REAL boolean that displays TRUE or FALSE?

Go with NULL consistently, throughout the entire application, everywhere, or don't. However, DO NOT MIX AND MATCH PARADIGMS and expect consistent results. Also, try not to rely upon CASE: there's very, very legitimate reason to depend upon that--especially for something as simplistic as what you're doing.

FYI, the only reason I can conceive why you would want this "indicator" field is so that you can test whether INDICATOR_A = 1. However, since you can test ASSET IS NULL, why even bother? NEVER introduce extraneous mechanisms when there is no overpowering reason to do so.

Answer 3

Try to use the function ASCII

ASCII ( character_expression )

Using this function you can understand what is the really character in the column Asset_Value: for example NULL value must have ASCII code: '00' Table with character ASCII code