difference between inner join and outer join

What's the difference between a LINQ to entity left-connected right connection and an inner join notation, and how to write with a lambda expression, which is more efficient?[Workaround]Left join right or connected this actually you don't need to care. Just write the query based on the mapping of the entity, and the fr

(4, ' IT ', 0); INSERT into employees values (1, ' WBQ ', 1,0), insert into employees values (2, ' Czh ', 2,0), insert into employees values (3, ' CHH ', 1,0); INSERT into employees values (4, ' Wal ', 2,0); INSERT into employees values (5, ' ddd ', 3,0); COMMIT;Here are the test examples--Lists department and employee information for Department ID 3, regardless of whether the department has an employee select D.depid,d.depname,e.empname from Departments D leave

Let's say we have two tables. Table A is the tables on the left. Table B is the tables on the right. Each has four records, of which two records name is the same, as follows: Let's look at the different joinsA tableID Name1 Pirate2 Monkey3 Ninja4 spaghettiTable BID Name1 Rutabaga2 Pirate3 Darth Vade4 Ninja 1.INNER JOIN SELECT * from TableA INNER

following on, the restriction condition of the right table will take effect. **************************************** **************************************** ** SQL statement 4: select a. *, B. * from a inner join B on A. ID = B. ID and A. type = 1; SQL statement 5: select a. *, B. * from a inner join B on A. ID = B

. **********************************************************************************SQL statement 4:select a. *, b.* from a innerJoinB on a.id = b.id and A.type = 1; SQL statement 5:select a. *, b.* from a innerJoinB on a.id = b.id where A.type = 1; SQL statement 6:select a. *, b.* from A, b where a.id = b.id and A.type = 1; SQL statement 7:select a. *, b.* from A, b where A.type = 1 and a.id = B.The result of the execution of these four statements is as follows: a. ID A.type b.id B.class-------

Calculate the total amountSelect sum (price * qty) from books;Query groups (the group by statement must be in select)Select sum (price * qty) from books group by pub;Incorrect case:This is not correct. As mentioned above, Aggregate functions cannot be combined with where.Select pub, sum (price * qty) from books where sum (price)> 30Therefore, we use the having clause for combination, as shown below:Select pub, sum (price * qty) from books group by pub having sum (price)> 500Queries that start wi

3.4, example 3.5, although the result set is the same, according to its SQL semantics, the execution process should be different. (I do not know the principle, here is not to delve into it) > Left Outer connectionSelect * from t_user u Left outer Join on = A.user_id; Multilayer outer Joins Select * from t_user

Join has a total of four internal and external Join inner join Left join Outer Join Right join Outer