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Nested Tables versus Index-by TablesThe Index-by tables and nested tables are just similar. For e.g. They have similar structure and their individual elements are accessed in the similar way (by using subscript notation). The main distinction is that the nested tables can be stored in a database column (and hence the word "nested table") while the index-by tables cannot.The Nested tables extend the functionality of the index-by tables by letting you SELECT,INSERT, DELETE, and UPDATE nested tables stored in the database. (Keep in mind, that index-by tables cannot be stored in the database). Some collection methods also operate only on the nested tables and varrays. For example, the built-in procedure TRIM cannot be applied to the index-by tables.Another merit of the nested tables is that an uninitialized nested table is automatically null (that is, the table itself is null, not its elements), while an uninitialized index-by table is simply empty. Therefore, you can apply the IS NULL comparison operator to the nested tables but not to index-by tables.Though, index-by tables also have some merits. For example, the PL/SQL supports implicit (automatic) datatype conversion between the host arrays and index-by tables (but not nested tables). Therefore, the most efficient way to pass collections to and from the database server is to use the anonymous PL/SQL blocks to bulk-bind input and output host arrays to the index-by tables.
Using SAVEPOINT The SAVEPOINT names and marks the present point in the processing of a transaction. Used with the ROLLBACK TO statement, the savepoints undo parts of a transac
Example of Alternative formulation as a table constraint Example: Alternative formulation as a table constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_
Projection in SQL - correct version Student StudentId is enrolled on some course. SELECT DISTINCT StudentId FROM IS_ENROLLED_ON In more complicated examples it is someti
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
Need for Dynamic SQL: You need dynamic SQL in the situations as follows: 1) You would like to execute a SQL data definition statement (like CREATE), a data control statemen
Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.
EXIT Statement You can use the EXIT statement to exit a loop. The EXIT statement has 2 forms: the conditional EXIT WHEN and the unconditional EXIT. With the either form, you
Consider the schema for FreeChecking Bank, that we designed given below. Translate the given ER schema into SQL CREATE TABLE statements (indicating primary key, unique and foreign
Managing Cursors The PL/SQL uses 2 types of cursors: implicit and explicit. The PL/SQL declares a cursor implicitly for all the SQL data manipulation statements, including th
Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )
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