"She bought what she needed last night" 与 "She bought whatev

1.She bought what she needed last night.
2.She bought whatever she needed last night.
whatever=no matter what
so:
1=she bought the things that she needed
2=she bought (all) the things that she needed.
句一是买了一些东西,但是需要的东西没全买.
句二是只要是需要的,就都买了.差别很大.
类似数学里面充分不必要和必要不充分的关系.