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MySQL笔记7

时间:2018-09-09 17:47:55      阅读:157      评论:0      收藏:0      [点我收藏+]

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";

 

MySQL笔记7

原文:https://www.cnblogs.com/Shinered/p/9614031.html

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