left-join

问题 I'm trying to do a left join in subsonic 3 using linq but it doesn't seem to work, I get a big error. var post = from p in Post.All() join q in Quote.All() on p.ID equals q.PostID into pq where p.ID == id.Value from qt in pq.DefaultIfEmpty() select new {p, qt}; I'm using subsonic 3, latest GIT version from Rob, but I'm getting an error, see below, when I try a left join. I have searched but I didn't found any solution. Can anyone explain to me why the error and how to fix it? Thanks

问题 See important new discoveries 1 and 2 at end of this explanation. I am running Postgres 9.1.3 and am having a weird left join issue. I have a table named consistent.master with over 2 million rows. It has a column named citation_id , and that column has no nulls. I can verify that with this: SELECT COUNT(*) FROM consistent.master WHERE citation_id IS NULL That returns 0 . Here's where it gets weird: if I LEFT JOIN this table to a temporary table, I get an error that I am trying to insert a

问题 See important new discoveries 1 and 2 at end of this explanation. I am running Postgres 9.1.3 and am having a weird left join issue. I have a table named consistent.master with over 2 million rows. It has a column named citation_id , and that column has no nulls. I can verify that with this: SELECT COUNT(*) FROM consistent.master WHERE citation_id IS NULL That returns 0 . Here's where it gets weird: if I LEFT JOIN this table to a temporary table, I get an error that I am trying to insert a

问题 Can I add some condition to the LEFT JOIN sql that Rails generate for the includes method? (Rails 4.2.1, postresql). I need to get all(!) the users with preloading ( not N+1 when I will puts in a view count of comments, posts and etc) of associations, but associations need to be filtered by some conditions. Example: User.includes(:comments) # => SELECT * FROM users LEFT JOIN comments ON ... This will return all the users and preload comments if they exists. If I will add some conditions for

问题 I have a query that looks something like this: SELECT orders.order_id, items.item_id, GROUP_CONCAT(graphics.graphic_id) AS graphic_ids FROM orders orders LEFT JOIN order_items items ON orders.order_id = items.order_id LEFT JOIN order_graphics graphics on graphics.item_id = items.item_id WHERE // etc GROUP BY items.item_id Orders can have zero or more items, and items can have zero or more graphics. The goal is to get all orders matching the WHERE condition, itemize them by order item, and

问题 I need to join 3 tables a,b,c and I know that only one row from the table most to the left has to appear in the end result. SELECT * FROM a LEFT JOIN b ON a.id = b.id LEFT JOIN c ON c.id2 = b.id2 WHERE a.id = 12; I have come up with the following query because it seems more efficient, but both queries take the same time to execute. Is this because the first query is optimized? Should I bother to choose the more efficient (second) query or stick to the first one because it's more readable?

问题 My query pulls results from several tables using a few LEFT JOIN s. It currently works fine. However, I now have to get two different fields from the same table column (but matching different conditions). I don't know how to make sure the correct column alias gets assigned from the correct LEFT JOIN. Make sense? So here's for example... SELECT table1.user_id, table2.value AS school, table2.value AS language FROM table1 LEFT JOIN table2 ON table2.user_id = table1.user_id AND table2.key =

问题 In Postgres, is there a way to perform a left join between tables linked by a junction table, with some filtering on the linked table? Say, I have two tables, humans and pets , and I want to perform a query where I have the human ID, and the pet name. If the human ID exists, but they don't have a pet with that name, I still want the human's row to be returned. If I had a FK relationship from pets to humans , this would work: select h.*, p.* from humans as h left join pets as p on p.human_id =

问题 When adding the line: LEFT JOIN core_records_sales as sales ON DATE(appointments.date) = DATE(sales.date_sold) To my query, it boosts the time for the script to run from about 8 seconds, to 2-3 minutes. Would there be some data causing this problem or am I not implementing the function correctly? I need to use DATE() because I need them to be the same day but the date fields are DATETIME 回答1: This is almost certainly an issue with the appointments.date field being indexed. Adding the use of

问题 Edit : People are having a hard time understanding what i want. So here's pretty pictures that explains it in excruciating detail. First join Transactions to Strange : The results so far Customer Invoice TransactionID Mass Length LeptonNumber ======== ======= ============= ==== ==================== ============ Ian One 1 Ian Judgement Spaulders 50 Ian One 1 Ian Glorious Breastplate 50 Chris Two 2 Chris Barenavel 2 Now attempt to join remaining rows with Down : The results so far Customer