Update: This article in my blog summarizes both my answer and my comments to another answers, and shows actual execution plans: IN vs. JOIN vs. EXISTS SELECT * FROM a WHERE a.c IN (SELECT d FROM b) SELECT a.* FROM a JOIN b ON a.c = b.d These queries are not equivalent. They can yield … Read more
You can’t do that with a LINQ joins – LINQ only supports equijoins. However, you can do this: var query = from e in entity.M_Employee from p in entity.M_Position where e.PostionId >= p.PositionId select p; Or a slightly alternative but equivalent approach: var query = entity.M_Employee .SelectMany(e => entity.M_Position .Where(p => e.PostionId >= p.PositionId));
The answer is NO difference, but: I will always prefer to do the following. Always keep the Join Conditions in ON clause Always put the filter’s in where clause This makes the query more readable. So I will use this query: SELECT value FROM table1 INNER JOIN table2 ON table1.id = table2.id WHERE table1.id = … Read more
I had a similar problem with several lookup tables joining to a large table with all id fields indexed. To monitor the effect of the joins on query time execution, I ran my query several times (limiting to first 100 rows), adding a Join to an additional table each time. After joining 12 tables, there … Read more
I’d probably use a LEFT JOIN, which will return rows even if there’s no match, and then you can select only the rows with no match by checking for NULLs. So, something like: SELECT V.* FROM voter V LEFT JOIN elimination E ON V.id = E.voter_id WHERE E.voter_id IS NULL Whether that’s more or less … Read more
SELECT <select_list> FROM Table_A A LEFT JOIN Table_B B ON A.Key = B.Key WHERE B.Key IS NULL Full image of join From aticle : http://www.codeproject.com/KB/database/Visual_SQL_Joins.aspx
JOIN t2 ON t1.id=t2.id AND t1.date=t2.date
You can simply add another join like this: SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id, images.filename FROM dashboard_data INNER JOIN dashboard_messages ON dashboard_message_id = dashboard_messages.id INNER JOIN images ON dashboard_messages.image_id = images.image_id However be aware that, because it is an INNER JOIN, if you have a message without an image, the entire row will be skipped. If this … Read more
Your error on the snippet of data you posted is a little cryptic, in that because there are no common values, the join operation fails because the values don’t overlap it requires you to supply a suffix for the left and right hand side: In [173]: df_a.join(df_b, on=’mukey’, how=’left’, lsuffix=’_left’, rsuffix=’_right’) Out[173]: mukey_left DI PI … Read more
Please read Routing Explicit Joins/Statements into Eagerly Loaded Collections. Then using contains_eager you can structure your query and get exactly what you want: authors = ( session.query(Author) .join(Author.books) .options(contains_eager(Author.books)) # tell SA that we load “all” books for Authors .filter(Book.title.like(‘%SQL%’)) ).all() Please note that you are actually tricking sqlalchemy into thinking that it has loaded … Read more