Sybase Joins

In SQL, a join is how you connect two or more tables to create a single result. As an example, we could connect together salesmen and their customers something like this...


This will pull out all the customers for each salesman...




Outer Joins

But suppose a salesman has no customers? He'll never appear in the report because the join shown above (known as an equi-join) will only produce output where a column in the first table matches a column in the second table. The way to overcome this is shown here...

Note the * character before the = sign. This turns the query into a 'left outer join' and might produce output like this...

There's a new row in the report for a salesman with no customer. Basically, the query returns every row in the table on the left side of the join together with any matches on the right. If there's no match, the query returns one row with the left hand table entry and a NULL for the right hand side.

You can, of course, reverse this to get a 'right outer join'...


which might return...


Showing that 'NewShop' hasn't been assigned to a salesman yet.  

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