Difference between Lookup, Join and Merge

Lookup stage supports:

• One stream input link
• 'n' reference links(n=1 to ...)
• one output link
• one optional reject link

Join stage supports:

• one Left set 
• one Right set
• 'n' intermediate links(n=0 to ....)
• one output link
• no reject links

Merge stage supports:

• one Master link
• n-update links(n=1 to ...)
• m-optional Reject links(m=0 to n)
• one output link

In Lookup we can apply Conditions. But in Join & Merge not possible to apply Conditions
In Lookup joining columns may not be with same name. But in Join & Merge Joining columns must be with same name