mysql多表查询数值为空null时处理成0

1.需求

在遇到多张表查询时，很可能查一个关联数值时，并没有这条关联记录，所以查询到的结果是null,通常需要把这个结果处理成0或者其他。如图

2.问题

部门是有11个的，但是其他几个部门没有人员，就不会展示出来，sql是这么写的

SELECT u.`name`, IFNULL(COUNT(*),0) as value
FROM
	units AS u
RIGHT JOIN unit_user AS uu ON u.id = uu.unitId
GROUP BY
	uu.unitId
ORDER BY
	u.sort ASC;

3.解决办法

SELECT u.id,u.`name`,ifnull(uu.count_id, 0)
FROM
	units AS u
LEFT JOIN (
	SELECT
		unitId,
		COUNT(id) AS count_id
	FROM
		unit_user
	GROUP BY
		unitId
) AS uu ON u.id = uu.unitId
ORDER BY
	sort ASC;

或者

SELECT
	u.`name`,
	(
		SELECT
			COUNT(id)
		FROM
			unit_user AS r
		WHERE
			r.unitId = u.id
	) AS userCount
FROM
	units AS u
LEFT JOIN unit_user AS r ON u.id = r.unitId
GROUP BY
	u.`name`
ORDER BY sort ASC;

结果：