A cross join produces a cartesian product between the two tables, returning all possible combinations of all rows. It has no on clause because you’re just joining everything to everything. A full outer join is a combination of a left outer and right outer join. It returns all rows in both tables that match the … Read more
Yes, see the example on Wikipedia. SELECT employee.*, department.* FROM employee LEFT JOIN department ON employee.DepartmentID = department.DepartmentID UNION ALL SELECT employee.*, department.* FROM department LEFT JOIN employee ON employee.DepartmentID = department.DepartmentID WHERE employee.DepartmentID IS NULL
Update 1: providing a truly generalized extension method FullOuterJoin Update 2: optionally accepting a custom IEqualityComparer for the key type Update 3: this implementation has recently become part of MoreLinq – Thanks guys! Edit Added FullOuterGroupJoin (ideone). I reused the GetOuter<> implementation, making this a fraction less performant than it could be, but I’m aiming … 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