Trying to find 3 separate counts within one column of a table, each with separate WHERE clauses. I've got 2 tables in the query, so one join. Thought this looked correct but it will not run:

SELECT stores.caption,
	 
COUNT (
	 		WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' 
			AND tasks.deleted_at IS NULL) 
	 		AS TaskTotal , 
	
 COUNT (
	 		WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' 
		  	AND tasks.deleted_at IS NULL 
			AND tasks.completed_at IS NULL) AS TaskOutstanding, 
	 
COUNT (
	 		WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' 	
			AND tasks.deleted_at IS NULL 
			AND tasks.completed_at IS NULL 
			AND tasks.deadline < '2019-05-16') AS TaskOverdue

	FROM tasks
	FULL JOIN stores ON tasks.store_id=stores.id
	GROUP BY stores.caption;