What is the use of derived table in SQL Server?
A derived table is a technique for creating a temporary set of records which can be used within another query in SQL. You can use derived tables to shorten long queries, or even just to break a complex process into logical steps.
What are the benefits of using a CTE over derived tables?
Derived tables are subqueries that are used in the FROM clause instead of named tables. I like using CTEs over derived tables because CTEs are so much easier to read. Derived tables can be nested and often are several layers deep, becoming difficult to read and understand.
What is difference between temp table and CTE?
Temp Tables are physically created in the tempdb database. These tables act as the normal table and also can have constraints, an index like normal tables. CTE is a named temporary result set which is used to manipulate the complex sub-queries data. This is also created in the tempdb database but not the memory.
Can a derived table be joined to a regular table?
Because you can treat derived tables like regular SQL Server tables, you can join two or more derived tables. Also, you can nest queries referencing a derived table inside of one another. A code sample in this part of the tutorial demonstrates this derived table capability for the enumeration of duplicate records in a data source.
How is a derived table treated in SQL Server?
This is because you can bury the complexity of a subquery in a derived table in a FROM clause and refer to subquery result column values in the derived table. Because you can treat derived tables like regular SQL Server tables, you can join two or more derived tables. Also, you can nest queries referencing a derived table inside of one another.
Why does Teradata use inner join in method 3?
Teradata’s optimizer quite possibly will re-write Method 3 to the same query plan as Method 2. Method 1 will result in an INNER JOIN because the qualification on the RIGHT table shouldn’t be in the WHERE clause but the ON clause of the OUTER JOIN condition.
How to improve the usefulness of the preceding result set?
One potential way to improve the usefulness of the preceding result set is to add currency name as a column. You can achieve this outcome by adding a left join of rows from the Currency table to the rows of the CountryRegionCurrency table in the preceding query.