php - 获取另一个表中特定行的一个表的平均值 php

Question

我正在尝试执行以下操作。

从名为“医院”的表中选择 id = hid 的医院。 向其中添加值“overall_ rating”并获取所有评级，并从另一个名为 h rating 的表中获取其平均值

这是我的查询

 $statement = $conn->prepare('SELECT hospital.*,(SELECT AVG(hrating.rating_h) FROM hrating WHERE hid = hospital.hid) as overall_rating WHERE hid=:hid LIMIT 1');

收到此错误

{"error":"SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE hid='44' LIMIT 1' at line 1"}

我哪里错了。

Answer 1

您的查询中似乎没有“FROM Hospital”位？

SELECT hospital.*,(SELECT AVG(hrating.rating_h) 
                   FROM hrating 
                   WHERE hid = hospital.hid) as overall_rating 
FROM hospital -- this line seems to be missing ??
WHERE hid=:hid LIMIT 1