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Hi @skateforlife3679, that is exactly the case, correct! The thing with join is, that we sometimes want the duplicate rows and sometimes not. But this behavior is not intuitive and we have to explicitly think about what is going on at the data level when our join criteria might not be unique. When we don't want the duplicates, we have to explicitly work our way around it (e.g. using DISTINCT, GROUP BY or String Aggregations). But, you explained it much shorter than me 😀... Have a nice day, Henning aka Don Data

Hi @@عليالعصفوري-ط4ض , I am not 100% sure I understand your question correctly. You can definitely loop over tables, which would be the SQL equivalent to arrays from programming. Yiu could either use CURSORs to loop over tables, or WHILE loops which fetch one row per loop. Conditions can be set using IF... THEN.... ELSE.... END. In general, while possible, in SQL you try to avoid loops and rather use so called set operations, which perform query logic over the whole table at once instead of row by row logic for performance reasons. Does this answer your question? Best wishes, Henning aka Don Data

@Don_Data My question is in real world app Like social media app if iwhat to send data like posts: { Id:1, Content : content , User:{ Id:1, Name: jack } } For all posts table with each user I fetch all posts the loops by it and fetch every user where primary = forigen Or i can fetch left join like this structur in some how

Hi @عليالعصفوري-ط4ض, if I understand correctly, you have two tables, Posts and Users in a relational database and want to expose the data as .json? The part of generating the json structure aside, to fetch the data you could query: SELECT p.Id AS PostId, p.Content, u.Name AS UserName FROM Posts p INNER JOIN Users u ON u.Id = p.UserId But I am not 100% sure if I understood you correctly. Without know the data structure on the database side, it is difficult to tell. Hope this helps to point you in the right direction.

@@Don_Data yes you under stand correctly if the query as you writing it will fetch as array of mixed data or left join row But i want the user data to be in sub array called user What i did was left join then fetch first table from db then fecth second table from db Then for loop push first of users in first of posts [user] , second in second... etc. Can i have finall result directly from data db without loop

Hi @عليالعصفوري-ط4ض, yes, you can create JSON string from SQL queries in most database engine. I have create a browser executable query. You can open it via the following link using T-SQL (e.g. Microsoft SQL Server). sqlfiddle.com/sql-server/online-compiler?id=542776f0-ff9f-42fa-8bbe-5e55304a092f If the link does not work, here is the code: SELECT 'Post 1' AS Id, 'First post of User 1' AS Content, 'User 1' As Userid INTO #Posts UNION SELECT 'Post 2' AS Id, 'Second post of User 1' AS Content, 'User 1' As Userid UNION SELECT 'Post 3' AS Id, 'First post of User 2' AS Content, 'User 2' As Userid UNION SELECT 'Post 4' AS Id, 'Second post of User 2' AS Content, 'User 2' As Userid SELECT 'User 1' AS Id, 'First User Name' AS Name INTO #Users UNION SELECT 'User 2' AS Id, 'Second User Name' AS Name SELECT p.Id AS Postid, p.Content, u.Id AS UserId, u.Name FROM #Posts p INNER JOIN #Users u ON u.id = p.UserId FOR JSON AUTO; I hope this brings you on the right track and you can avoid the loops, Henning

Hi @vietphu2804, glad that this video is helpful for you!

Hi Carlos, wow, thanks for sharing all this. I am still not 100% on top of the commenting functionality here so I did miss it. I am happy to read this and I am confident that you will make your transition to the data analytics space. You just made me smile. Making this RUclips channel sometimes feels like doing all the effort in vain. Thanks a lot! 😀