Oak tables are beautiful additions to a home, and they add a functional purpose. Oak is generally sturdy and lasts a long time; however, it needs to be maintained and given a little bit of moisture or it can dry out. If it does dry out, there is a risk of cracking. You can repair the cracks with patience and proper supplies.
Set a wedge in the split, and push it apart slightly.
Brush out the split to remove dust.
Squirt wood glue on the brush, and spread it in the split. If you cannot get the split open wide enough, squirt the glue into the crack.
Remove the wedge, and press the wood together. Set up clamps to hold the table together while the glue dries. Wipe off the excess glue that squirts out, and leave it overnight to dry.
Remove the clamps, and use a putty knife to carefully peel off glue that continued to come out from the split while it was clamped.