What diffrence bitween these two mysql operators

Can any one tell me What diffrence bitween these two mysql operators :-

<=> and =

Both are getting same results. Are they same in use.

select s.dwt,s.shipnam from tbl_ship s
where s.dwt >= 1 and s.deleted = 'N'
and s.dwt = 11000
group by s.co_cod

and

s开发者_运维知识库elect s.dwt,s.shipnam from tbl_ship s
where s.dwt >= 1 and s.deleted = 'N'
and s.dwt <=> 11000
group by s.co_cod

Thanks.

<=> is NULL-safe equal to operator.

It is null safe equal to operator :

http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#operator_equal-to

From mysql documentation :

mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
        -> 1, 1, 0
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
        -> 1, NULL, NULL

<=> NULL-safe equal to operator

That's why. You probably wanted to use <> or != to test for inequality.

http://dev.mysql.com/doc/refman/5.1/en/comparison-operators.html#operator_equal-to