Wedding DJ vs Club DJ
The main difference is that in a wedding scenario the attention is on the bride & groom whereas the in a club environment the attention is on the DJ. Although the music is a very important part in a wedding, guests will attend the reception to pay their respect to the couple.
The wedding DJ is not the star of the show. Besides music, the wedding DJ is responsible for conducting the schedule and the flow of the wedding and reception. In weddings there will be all ages from kids to grand fathers and the music has to reflect so that everyone enjoys themselves.
Dressed smartly - Suited
Music Selection - the couple gets to pick their favourite music to be played during the night
Plays dinner and conversational music
Make announcements - Introduce the family members properly
All equipment provided
Ceremony Service - wireless microphones and music
Crowd Reading - A professional DJ will know how to get people to the dance floor and keep them interested by changing genres and mixing it up.
Free Consultation -Meet up in person or talk via email to understand exactly what you are looking for and make it happen
At a club all people are around the same age and have very similar music tastes and normally goes on till the early hours of the morning.
Artists - people go to see the DJ perform and hear his music.
Here is video on local TV programme discussing the key roles of a DJ amongst other things (In Maltese):
So to conclude, there is a lot of difference between the two but fundamentally they are both doing the same thing and that is: Playing the music and making everyone happy.