力扣sql入门篇(五)

1 组合两个表

1.1 题目内容

1.1.1 基本题目信息

1.1.2 示例输入输出

1.2 示例sql语句

SELECT firstname,lastname,IFNULL(city,null) city,IFNULL(state,null) state
FROM Person p
LEFT JOIN Address a
ON p.personid=a.personid;

1.3 运行截图

2 进店却未进行过交易的顾客

2.1 题目内容

2.1.1 基本题目信息

2.1.2 示例输入输出

2.2 示例sql语句

SELECT v.customer_id customer_id,count(*)  count_no_trans
FROM Visits v
LEFT JOIN Transactions t
ON v.visit_id=t.visit_id
WHERE t.transaction_id is null
GROUP BY v.customer_id
ORDER BY count_no_trans desc;

2.3 运行截图

3 文章浏览I

3.1 题目内容

3.1.1 基本题目信息

3.1.2 示例输入输出

3.2 示例sql语句

SELECT distinct author_id id
FROM Views
WHERE author_id=viewer_id
ORDER BY id asc;

3.3 运行截图