需要帮助来创建单个Mysql查询

Question

I have a table that stores the names of people in a users circle. Relevant fields are: username & circleMember

I have another table that that stores all listings create by individual users.

My app sends a request to the server providing the active users username.

I need a query that will SELECT from circle circleMember WHERE username = ?username and then SELECT from listings * WHERE username = (the result of first query) the username, circleMember combinations are stored on individual rows so there will be multiple rows for each username.

table circle
 - circleId (int)
 - username (varchar) 
 - circleMember (varChar)

table listings
- listingId (int)
- username (varchar) 
- image (varchar) 
- title (varchar) 
- price (decimal 15,2) 
- description (varchar) 
- location(varchar)

My current script gets all listings from the database and presents them in Card Views. The result I am looking for is that a user will only see listings from usernames in their circle.

I have tried various combinations of single queries from posts on this site but apparently lack the proper syntax to make it work. Can this be done in a single query or do I need one to get results and then another to iterate through the results?

Answer 1

So I think you want a simple JOIN

SELECT * FROM circle 
JOIN listings ON circle.username = listings.username 
WHERE circle.circleId = (SELECT circleId FROM circle WHERE username = <username> limit 1)

Where <username> is replaced with some quoted string.

http://dev.mysql.com/doc/refman/5.7/en/join.html

no clue what 'circle circleMember is supposed to be

Answer 2

Is this what you mean?

SELECT * FROM listings
JOIN circle ON circle.circleMember = listings.username 
WHERE circle.username = "my_user_name"