Net ionic equation with only aqueous ions
If you have a balanced equation like the following:

$$\ce{NaCl_{(aq)} + KBr_{(aq)} -&gt; NaBr_{(aq)} + KCl_{(aq)}}$$

and the solubility products for all the species are big enough that there's essentially no solid, there's really no distinction between the left and right sides of the equation. It's a balanced equation, but nothing has changed. We started with $\ce{Na+_{(aq)} + K+_{(aq)} + Br^{-}_{(aq)} + Cl^{-}_{(aq)}}$ in solution and we still have that on the right side. So there's really not a net ionic equation because there's no net change.