![]() It speeds up development and reduces your chance of errors.This tip is part of a series on using different kinds of SQL Server code modules. ![]() For the latter group, there is nothing wrong with using the tools available to you. For the former group, hopefully this article will show you something new. Which when executed results in both Orphans being returned, because again, they have no matching record in the Parents table:įrom the questions posted to newsgroups and forums, it seems to me that plenty of people are either unaware of the existence of the Query Designer, or don't use it because they consider it some kind of cheating. If we type "IS NULL" in the Filter column against the AdultID column of the Children table to the LEFT OUTER JOIN example, we end up with the following diagram and SQL:Īnd executing this results in Jimmy being returned on his own as the only record in the Parents table that doesn't have a matching record in the Children table:Ĭonversely, doing the same thing to the AdultID in the Adults table in the RIGHT OUTER JOIN example: Applying this as a filter to a JOIN query is very useful to finding records in one table that have no related records in the second table. If you study the results of, for example, the LEFT OUTER JOIN, you will notice that Jimmy was returned with a value of NULL in the Children table side of the resultset. There are some obscure uses for CROSS JOINS, including the creation of test data, but generally, they are not used. That means that every row in one table is matched to every row in the other table: We get a CROSS JOIN, which results, when executed, in the Cartesian product of both tables - 5 parents x 8 children = 40 rows. This returns all records from both sides of the relationship, regardless of whether there are matching records: Selecting both options from the JOIN property menu gives us a FULL OUTER JOIN: I think he just hates kids.įULL OUTER JOIN - All Parents and all children When executed, our orphans appear in the ChildName column, with NULL against the parent column. The right hand side (or perhaps the RIGHT OUTER side?)of the diamond is now filled out, and the SQL changes to reflect this: We deselect "Select All Rows from Parents", and select "Select All Rows from Children" instead. RIGHT OUTER JOIN - All children, and their parents if they have any In the case of Jimmy, he has NULL against the ChildName column, because he has no children. It also returns all the children that have parents. When this is executed, the LEFT OUTER JOIN returns all the parents (including Jimmy), irrespective of whether they have children or not: If we select "Select All Rows from Parents", the left hand side of the diamond fills out, and some new SQL is generated: Right-clicking on the diamond in the middle of the Join line in the query designer reveals a context menu with some options for the JOIN. LEFT OUTER JOIN - All Parents, and their children if they have any INNER JOIN only returns rows from the two tables where there are matches based on the JOIN-predicate, which in this case is where Parents.AdultID has a matching record in Children.AdultID. So who's missing? Batchelor Jimmy is nowhere to be seen (because he has no children) and nor are our orphans, Sam and Ian. ![]() Selecting AdultName and ChildName in the repsective columns generates the following SQL:Īnd when the SQL is executed, all parents with children are returned: However, you can simply drag AdultID in the Children table, and drop it onto the AdultID in the Parents table to create the relationship. If they are not automatically joined (by the line that appears between the tables) you have not set AdutlID in the Children table as a foreign key. If we open up the Query Designer in Sql Server Management Studio, and add the 2 tables, they are joined on the AdultID by default using an INNER JOIN. Children are related to Parents by the AdultID. This is how they appear in database tables: Parents and Children.
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