Coalesce - co-a-lesce - verb
	- co + alesce ( grow)。come together to form one mass or whole. 合并,兼并
 
	- In IT
	
		- SQL,
		
			- The COALESCE() function returns the first non-null value in a list.
 
		
		 
		- ServiceNow,
		
			- A field marked with "coalesce" in the transform map means if a record with data in the "coalesce" field exists, then update, else insert.