MySQL笔记7

1. Inner Joints 表示链接两个表格共有部分。(Inner  Joints)

当两个表格的列名相同时，为避免歧义，需指定从哪个表格进行引用的说明。

%%sql 
SELECT d.dog_guid AS DogID, d.user_guid AS  UserID, AVG(r.rating) AS AvgRating,
        COUNT(r.rating) AS NumRatings, d.breed, d.breed_group, d.breed_type
FROM dogs d, reviews r
WHERE d.dog_guid=r.dog_guid AND d.user_guid=r.user_guid
GROUP BY UserID, DogID, d.breed, d.breed_group, d.breed_type
HAVING NumRatings >= 10
ORDER BY AvgRating DESC
LIMIT 200；

2.从多个表进行结合。

SELECT c.user_guid AS UserID, u.state, u.zip, d.dog_guid AS DogID, d.breed, d.breed_type, d.breed_group
FROM dogs d, complete_tests c, users u
WHERE d.dog_guid=c.dog_guid 
   AND c.user_guid=u.user_guid
   AND c.test_name="Yawn Warm-up";