I See Null Instead Of Content In Some. RogerWang - Good question. The COALESCE function.
It means you have never set a value for your variable but empty means you have set value to your String for instance see the following example. Here str1 is null meaning that you have defined it but not set any value for it yet but you have defined str2 and set empty value for it so it has a value even that value is. In other words the SQL standard insists that you cannot use NULL or NULL and instead should use IS NULL or IS NOT NULL.
The IF function combined with the IS NULL or IS NOT NULL operator.
Tony Hoare the inventor of the null pointer we all love and hate has called null his Billion Dollar Mistake and some. There have been a number of opinions about this published already including Null References The Billion Dollar Mistake presentation by Tony Hoare and the entire Object Thinking book by David West. It isnt just a comparison with NULL that will always return NULL. Object b null.
