
Although many Mormons don't realize it, this particular verse causes a problem with their doctrine. Let's go through, step-by-step, the root of these problems. First, it comes from their doctrine of the Trinity:
I have always declared God to be a distinct personage, Jesus Christ a separate and distinct personage from God the Father and the Holy Ghost was a distinct personage and a Spirit: and these three constitute… three Gods. (Teachings of the Prophet Joseph Smith, p. 190)
Mormons give names to the first two Personages of their Trinity: Elohim and Jehovah. To the Mormon, Elohim and Jehovah are two different gods. Elohim (God the Father) is separate from Jehovah. And who do they consider Jehovah to be? That would be Jesus in the Old Testament. See, Mormons believe that when you see the tetragrammaton (Hebrew: YHWH, or LORD in all caps) in the Old Testament, this refers to Jesus. But whenever you see the word 'God' (Hebrew: Elohim), this refers to God the Father.
I will give them this: that when you see the word YHWH, it can indeed be referring to Christ, given that He is the second person in the (Orthodox) Trinity. Colossians 1:16


However, let us consider Psalm 110:1-2


But how does the Mormon interpret this passage? Does Jesus tell Himself to sit at His own right hand? "Jehovah (Jesus) said to my Lord (Jesus), "Sit...'"?
If you are reading these passages through the eyes of an unbeliever, or someone with a skewed understanding of the Trinity, then this seems to be a contradiction. And for the Mormon, it is. However, for those of us who hold to the orthodox view of the Holy Trinity (although not always understanding it), these passages are complementary to one another.
Now, here is where the dilemma lies for the Mormon in Psalm 97:9
