This is an example of the greatest-n-per-group problem that has appeared regularly on StackOverflow. Here’s how I usually recommend solving it: SELECT c.*, p1.* FROM customer c JOIN purchase p1 ON (c.id = p1.customer_id) LEFT OUTER JOIN purchase p2 ON (c.id = p2.customer_id AND (p1.date < p2.date OR (p1.date = p2.date AND p1.id < p2.id))) … Read more
Performance wise, they are exactly the same (at least in SQL Server). PS: Be aware that the IMPLICIT OUTER JOIN syntax is deprecated since SQL Server 2005. (The IMPLICIT INNER JOIN syntax as used in the question is still supported) Deprecation of “Old Style” JOIN Syntax: Only A Partial Thing
It goes something like: from t1 in db.Table1 join t2 in db.Table2 on t1.field equals t2.field select new { t1.field2, t2.field3} It would be nice to have sensible names and fields for your tables for a better example. 🙂 Update I think for your query this might be more appropriate: var dealercontacts = from contact … Read more
The answer is yes, you can. Try it like this: UPDATE TABLE_A a JOIN TABLE_B b ON a.join_col = b.join_col AND a.column_a = b.column_b JOIN TABLE_C c ON [condition] SET a.column_c = a.column_c + 1 For a general update join: UPDATE TABLEA a JOIN TABLEB b ON a.join_colA = b.join_colB SET a.columnToUpdate = [something]
DELETE TableA FROM TableA a INNER JOIN TableB b ON b.Bid = a.Bid AND [my filter condition] should work
I find that if you’re familiar with SQL syntax, using the LINQ query syntax is much clearer, more natural, and makes it easier to spot errors: var id = 1; var query = from post in database.Posts join meta in database.Post_Metas on post.ID equals meta.Post_ID where post.ID == id select new { Post = post, … Read more
As of Mongo 3.2 the answers to this question are mostly no longer correct. The new $lookup operator added to the aggregation pipeline is essentially identical to a left outer join: https://docs.mongodb.org/master/reference/operator/aggregation/lookup/#pipe._S_lookup From the docs: { $lookup: { from: <collection to join>, localField: <field from the input documents>, foreignField: <field from the documents of the … Read more
As stated in “Perform left outer joins”: var q = from c in categories join p in products on c.Category equals p.Category into ps from p in ps.DefaultIfEmpty() select new { Category = c, ProductName = p == null ? “(No products)” : p.ProductName };
This post aims to give readers a primer on SQL-flavored merging with Pandas, how to use it, and when not to use it. In particular, here’s what this post will go through: The basics – types of joins (LEFT, RIGHT, OUTER, INNER) merging with different column names merging with multiple columns avoiding duplicate merge key … Read more
You don’t have full joins in MySQL, but you can sure emulate them. For a code sample transcribed from this Stack Overflow question you have: With two tables t1, t2: SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.id UNION SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id The query above … Read more