Updating specific row in cursor
Although some arbitrary conditions may be used, nevertheless the equi-join is most commonly used because this operation reproduces a certain entity split by two entities as a result of a normalization process.
Even though different tables have columns with the same names, the dot notation is needed for uniqueness: Note that in this case the Product qualifier may not be already used in other clauses of the SELECT statement.
For better control, the result includes the model number both in the PC table and in the Product table: The LEFT JOIN implies that all the rows from the first (left) table are to be in the result set along with the rows for which the predicate evaluates to true.
In so doing, the non-matching colunm values in the right table are returned as null values. Find all PC models, makers, and prices: It is essential that using the WHERE clause is indispensable for sampling only PC makers as compared with the previous example.
The SELECT operator syntax given at the end of the previous chapter shows that more than one table may be pointed in the FROM clause.
A table listing that does not use WHERE clause is practically unused because this produces the relational operation of the Cartesian product of the tables involved.
For example, the tables As a rule, the table listing is used with the condition of joining records from different tables in the WHERE clause.
While refreshing the screen quickly is generally desirable, the buffers required do consume system memory.
If memory limitations occur, you can set while the delete function executes, after which the object no longer exists.
Here is the result set: Because models 21 in the Product table are absent in the PC table, the columns of the PC table contain NULL.
The RIGHT JOIN is the reverse of the LEFT JOIN, i.e.
The INNER and OUTER keywords may be omitted, because the outer join is uniquely defined by its type: LEFT, RIGHT, or FULL, whereas the inner join is simply refered to as JOIN.