Meaning of phrase

Can anyone tell me the meaning of the phrase
"if wishes were horses, pigs would fly."

Thanks in anticipation.

You've got two separate phrases muddled there. "Pigs might fly" is an ironic response to an unlikely proposition. For example, "Iraq has WMD that they might use to attack London" - "Yes, and pigs might fly".

The other is "If wishes were horses then beggars would ride", which is pretty much self-explanatory.