It's more complicated then that.
For some it should be complete alcohol abstinence and for others moderation is okay. For example, if you have a weakness with alcohol and know that you are easily tempted to fall into drunkenness, then avoid it all together. But if you are one who can drink one glass and will not fall into the temptation of drunkenness, then moderation is okay for you. If you are unsure, and have doubts about self control and alcohol, don't even try it.