这两种约束好象都能使TABLE的某一列的值或多列的组合值是唯一的，请问这两种约束有其它的区别？？

这是SYBASE文档中的一段：
unique – constrains the values in the indicated column or columns so
that no two rows can have the same non-null value. This
constraint creates a unique index that can be dropped only if the
constraint is dropped. You cannot use this option along with the
null option described above.
primary key – constrains the values in the indicated column or columns
so that no two rows can have the same value and so that the value
cannot be NULL. This constraint creates a unique index that can
be dropped only if the constraint is dropped.

看起来其区别是：
unique：允许NULL值
primary key：不允许NULL值

unique：列中可以有null值，一个表中可以有多个
primary key：列中不可以有null值，一个表中最多只能有一个，而且建议要有一个。

其它的基本一样