Building a "floating" platform
Wouldn't need to have a pillar. Would need at least a diagonal brace securely mounted to the wall framing. Unless, that is, you can build a boxed platform rigid enough to carry that stress without flex. 

I'd use 3-5 heavy duty brackets like this.You'd barely be able to see them under your platform, leaving it with a floating appearance. Leave the end one 20-40cm from the end to help hide it visually. 

I've built several such surfaces with good results using 2-1/2" lag screws. The brackets should ideally reach about 2/3 the way to the front or could be extended with structural top rails.



This question comes along regularly in various forms. Here are a few. 

How can I support a desk without legs or brackets

How can I mount a desk on a wall with L-brackets?

How is a floating desk top supported against the wall?

DIY Floating Desk in New Build Home

What is the ideal method of supporting a 27&quot; deep floating desk across 10 feet of wall?