A post and deck combination for a shelf assembly includes a hollow vertical post having an outer wall with slots at different heights. Each slot has a positioning portion. A coupling board is disposed on an edge of a deck and includes a first insertion groove. A coupling member includes a columnar portion interconnected between first and second ends thereof and having a first section with a diameter smaller than a width of each positioning portion and a second section received in the first insertion groove. The coupling member extends through one of the slots. The positioning portion of the one of the slots is located at the first section. The first insertion groove is coupled with the first end of the coupling member. A first receiving end of the first insertion groove is located on an inclined guiding face of the second section.