想跟小哥哥请教下MongoDB的查询语句,这问题已经难住我一天啦!!!?

想请教下下面这句sql语句怎么转换成MongoDB呀,在网上找了一天也没能解决

select count(*) from A left join B on A.id = B.a_id where B.name like '%xxx%'

那你一定没找对

db.A.find( { name: /xxx/ } ).count()

SELECT
COUNT(*)
FROM A
LEFT JOIN B ON A.id=B.id
WHERE
B.name LIKE '%xxx%'