Database Reference
In-Depth Information
Figure 6.39
Use inner join to select data from two tables.
Figure 6.40
Use left outer join to select data from two tables.
selects all the weekdays from the left table that may or may not be assigned classes from the right
table.
As you can see, LEFT OUTER JOIN is used to link the two tables. Since no classes are sched-
uled on Friday, Saturday, and Sunday, the corresponding class id values from the right-hand side
table CLASS are NULL.
Reversely, you can use a
right outer join
that includes all rows from the right table and place
NULL values in the rows from the left table that do not match the corresponding rows from the
right table. When joining two tables with a right outer join, use the phrase RIGHT OUTER
JOIN in the query. For a
full outer join
, the selection result includes all rows from both tables no
matter if there is a match or not.
