sql - Difference between NULL and Blank Value in Mysql

Question

I have to check for a value of a particular Column named RESULT is blank or not.

When I check with if RESULT IS NULL, the query failed, but When I checked RESULT='', it worked.

What is difference between two.

please explain.

"UPDATE RLS_TP_2012_03 a, RLS_TP_2012_03 b SET a.COMMENT=b.COMMENT where b.TCODE='T1199' and  a.GROUPNAME='xyz' and a.HLABNO=b.HLABNO and a.RESULT =''; ";   
"UPDATE RLS_TP_2012_03 a, RLS_TP_2012_03 b SET a.COMMENT=b.COMMENT where b.TCODE='T1199' and  a.GROUPNAME='xyz' and a.HLABNO=b.HLABNO and a.RESULT is NULL; "

Answer 1

1. NULL is an absence of a value. An empty string is a value, but is just empty. NULL is special to a database.

2. NULL has no bounds, it can be used for string, integer, date, etc. fields in a database.

3. NULL isn't allocated any memory, the string with NULL value is just a pointer which is pointing to nowhere in memory. however, Empty IS allocated to a memory location, although the value stored in the memory is "".