How to limit results of a LEFT JOIN

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Take the case of two tables: tbl_product and tbl_transaction. tbl_product lists product details including names and ids while tbl_transaction lists transactions involving the products and includes dates, product-ids, customers etc.

I need to display a web-page showing 10 products and for each product, the last 5 transactions. So far, no LEFT JOIN query seems to work and the subquery below would have worked if mysql could allow the tx.product_id=ta.product_id part (fails with Unknown column 'ta.product_id' in 'where clause': [ERROR:1054]).

SELECT  
ta.product_id,  
ta.product_name,  
tb.transaction_date  
FROM tbl_product ta  
LEFT JOIN (SELECT tx.transaction_date FROM tbl_transaction tx WHERE tx.product_id=ta.product_id LIMIT 5) tb
LIMIT 10

Is there a way to achieve the listing I need without using multiple queries in a loop?

Edit: This is exactly what I need from MySQL:

SELECT ta.product_id, ta.product_name, tb.transaction_date ...  
FROM tbl_product ta  
LEFT JOIN tbl_transaction tb ON (tb.product_id=ta.product_id LIMIT 5)  
LIMIT 10

Of course this is illegal, but I really wish it wasn't!

This is where ranking functions would be very useful. Unfortunately, MySQL does not yet support them. Instead, you can try something like the following.

Select ta.product_id, ta.product_name
    , tb.transaction_date
From tbl_product As ta
    Left Join   (
                Select tx1.product_id, tx1.transaction_id, tx1.transaction_date
                    , (Select Count(*)
                        From tbl_transaction As tx2
                        Where tx2.product_id = tx1.product_id
                            And tx2.transaction_id < tx1.transaction_id) As [Rank]
                From tbl_transaction As tx1
                ) as tb
        On tb.product_id = ta.product_id
            And tb.[rank] <= 4
Limit 10

Limit left join for multiple rows, What version of MySQL are you using? MySQL 8 supports LATERAL which you need to be able to refer to i from the derived table: SELECT i. SELECT * FROM table1 LEFT JOIN (SELECT * FROM (SELECT *, ROW_NUMBER() OVER(PARTITION BY assignmentgroup ORDER BY assignmentgroup) AS Seq FROM table2) a WHERE Seq = 1) v ON assignmet = v.assignmentgroup. share. Share a link to this answer. Copy link.

It fails because when you put parenthesis around your query and give it the alias "tb" you have created a derived table. Your derived table has no knowledge of the tbl_product table having alias "ta"

Try using ON or WHERE outside of the derived table, then reference that table using the alias" tb" you provided

EDIT:

The use of "LIMIT" limits the results of the query in its entirety. While you have "LIMIT 10" what you actually want is 50 rows (or less if there are fewer than 5 historical), is that right?

10 products, joined to 5 historical records, returning 50 total rows.

In this case, you can have a single query solution be joining the product table to itself in a derived table having "LIMIT 10"

Such as:

SELECT *
FROM tbl_product ta
JOIN (SELECT * FROM tbl_product tz WHERE tz.product_id = ta.product_id LIMIT 10) tc
LEFT JOIN (SELECT tx.transaction_date FROM tbl_transaction tx 
    WHERE tx.product_id=ta.product_id LIMIT 5) tb

You could also us "in" and specify the top 10 such as:

SELECT *
FROM tbl_product ta
LEFT JOIN (SELECT tx.transaction_date FROM tbl_transaction tx 
WHERE tx.product_id=ta.product_id LIMIT 5) tb 
WHERE ta.product_id IN 
  (SELECT z.product_id FROM tbl_product z LIMIT 10)

LEFT JOIN but only return one record, Hi, I have a table of products and I also have a table of images. Each product can have multiple (unlimited) images assigned to it. When I view  SELECT * FROM tbl_product ta JOIN (SELECT * FROM tbl_product tz WHERE tz.product_id = ta.product_id LIMIT 10) tc LEFT JOIN (SELECT tx.transaction_date FROM tbl_transaction tx WHERE tx.product_id=ta.product_id LIMIT 5) tb You could also us "in" and specify the top 10 such as:

Edit:

If you want to enforce a limit on each product I would separate it into two queries.

First get a list of 10 products and then run another query for each of those returning the last five transactions.

SQL JOINs, It then limits the results to only the ones whose song name start with the The LEFT JOIN keyword returns all the rows of the table on the left  When using postgres you can use the DISTINCT ON syntex to limit the number of columns returned from either table. Here is a sample of the code: SELECT c.id, c.title, p.id AS product_id, p.title FROM categories AS c JOIN ( SELECT DISTINCT ON(p1.id) id, p1.title, p1.category_id FROM products p1 ) p ON (c.id = p.category_id)

I found way to make LEFT JOIN with subquery, sorted and limited, its works on RDS Amazon, MariaDB v10.2

LEFT JOIN activities last_activity ON last_activity.id = ( 
     SELECT id FROM activities 
     WHERE contester_id = contesters.id AND `type` IN ({$last_activity_types}) 
     ORDER BY id DESC LIMIT 1 
)

All others ways to make LEFT JOIN with GROUPING and SORTING didn't works for me. This example is working exception.

SQL LEFT JOIN Keyword, Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, PHP, Python, Bootstrap, Java  The LEFT JOIN keyword returns all records from the left table (table1), and the matched records from the right table (table2). The result is NULL from the right side, if there is no match. LEFT JOIN Syntax

Use Oracle FETCH to Limit Rows Returned by a Query, SELECT product_name, quantity FROM inventories INNER JOIN products USING(product_id) ORDER BY quantity DESC LIMIT 5;. In this example, the ORDER  LEFT JOIN table2 t2 ON (t2.thing = t1.thing) to: LEFT JOIN table2 t2 ON (t2.p_key = (SELECT MIN(t2_.p_key) FROM table2 t2_ WHERE (t2_.thing = t1.thing) LIMIT 1)) the condition that connects t1 and t2 is moved from the ON and into the inner query WHERE. the MIN(primary key) or LIMIT 1 makes sure that only 1 row is returned by the inner query.

SQL LEFT JOIN: A Comprehensive Guide to LEFT JOIN in SQL, The table B also has four rows 3, 4, 5, 6. When we join table A with table B, all the rows in table A (the left table) are included in the result set whether there is  Introduction to SQL LEFT JOIN clause In the previous tutorial, you learned about the inner join that returns rows if there is, at least, one row in both tables that matches the join condition. The inner join clause eliminates the rows that do not match with a row of the other table.

SQL Server LEFT JOIN By Practical Examples, If no matching rows found in the right table, NULL are used. The following illustrates how to join two tables T1 and T2 using the LEFT JOIN clause: SELECT​  Introduction to MySQL LEFT JOIN. The LEFT JOIN allows you to query data from two or more tables. Similar to the INNER JOIN clause, the LEFT JOIN is an optional clause of the SELECT statement, which appears immediately after the FROM clause. Suppose that you want to join two tables t1 and t2.

Comments
  • you have no "ON" clause for your join?
  • Even with the ON clause, it still fetches more than 5 transactions. If I remove the tx.product_id=ta.product_id and modify to LEFT JOIN (*my limiting sql*) tb ON tb.product_id=ta.product_id, still not what I want~
  • Does your transaction table tbl_transaction have an id?
  • @gnarf Yes, there's a transaction_id column
  • Thanks for the response, Thomas. Yes, tbl_transaction has an AUTO_INCREMENT column as the primary key. I tried your proposal (although I don't quite understand it fully) and I got a list of the products but without any transactions. Why the self-join (on tbl_transaction [tx >-< tx2])? Could you please take me through the logic of the sub-query?
  • @eddy edu - The gist of it is to impose a ranking on the transactions by product. To that end, I compare the transaction table against itself to find the number of transactions for a given product earlier than a given row. The earliest row for a product should produce a count of zero. Now, if you are getting odd results, I have a couple of questions. First, can transaction date be null? Second, can transaction date be duplicated (two rows for the same product_id and date)?
  • transaction_date cannot be NULL. transaction_date can be duplicated (one product can have multiple transactions for a given date). I get the need to rank transactions by product (so that I can 'group' my transactions by products), I just need to see how the date column comes in.
  • @eddy edu - Ok. I've updated my post. Instead of looking for Count(Distinct tx2.Id), I changed it to Count(Distinct tx2.transaction_date). In short, I'm using transaction_date to rank the transaction rows. I do that by finding the number of other transaction rows with an earlier date. The earliest date for a given product should produce zero.
  • @eddy edu - It occurs to me that you might run into a problem with gaps in the transaction dates. Am working on a solution now.
  • After modifying (removing the tbl_product reference in the sub-query and adding it in an ON clause) the query works OK but the LIMIT seems only to apply to the first product i.e. I get a list of 10 product with the first one having 5 transactions but all the others have none.
  • Again the answer is because if your derived table. The "LIMIT" in the derived table is unrelated to the "LIMIT" in the entire query. How about some sample data?
  • Edited my answer to better explain
  • This one fails with a cryptic error that is only fixed by having an ON clause. And after the 'fix', the result-set only contains the first product with 5 transactions - other products are ignored.
  • I considered that but I'm sure there's a one-query solution to this! There just has to be!