'O God' in the Bible

So do God to Abner, and more also, except, as the LORD hath sworn to David, even so I do to him;

And when all the people came to cause David to eat meat while it was yet day, David sware, saying, So do God to me, and more also, if I taste bread, or ought else, till the sun be down.

Therefore Thou hast been great, Jehovah God, for there is none like Thee, and there is no God save Thee, according to all that we have heard with our ears.

So David made prayer to God for the child; and he took no food day after day, and went in and, stretching himself out on the earth, was there all night.

And it cometh to pass, David hath come unto the top, where he boweth himself to God, and lo, to meet him is Hushai the Archite, his coat rent, and earth on his head;

The king was deeply moved and went to the upper room over the gate and wept [in sorrow]. And this is what he said as he walked: “O my son Absalom, my son, my son Absalom! How I wish that I had died instead of you, O Absalom, my son, my son!”

In straits to me I will call Jehovah, And to God will I call, And he will hear my voice from his temple, And my cry in his ears.

For who God besides Jehovah? And who a rock besides our God?