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SQL Pseudocolumns
The PL/SQL recognizes the following SQL pseudocolumns, that returns the specific data items: LEVEL, NEXTVAL, CURRVAL, ROWID, & ROWNUM. The Pseudocolumns are not actual columns in a table but they behave as columns. For illustration, you can select values from a pseudocolumn. Though, you cannot insert into, update, or delete from a pseudocolumn. The pseudocolumns are also allowed in the SQL statements, but not in the procedural statements.
Left and Right Joins LEFT OUTER JOIN can be used when you want to retrieve the data from the main table (table1) even if there is no match in other tables (table_2, table_3...
Using NOT NULL Besides assigning an initial value, the declarations can impose the NOT NULL constraint, as the example below shows: acct_id INTEGER(4) NOT NULL := 9999; You ca
Using the BULK COLLECT Clause The keywords BULK COLLECT specify the SQL engine to bulk-bind output collections before returning them to the PL/SQL engine. You can use these ke
Using ROLLBACK The ROLLBACK statements end the present transaction and undo any change made during the transaction. The Rolling back is helpful for two reasons. Firstly, if yo
Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1
NULL Statement The NULL statement clearly specifies in action; it does nothing other than to pass control to the next statement. It can, though, improve the readability. In a
What are 3 good practices of modeling and/or implementing data warehouses?
BETWEEN Operator The operator BETWEEN, tests whether the value lies in a specified series. That means "greater than or equivalent to low value and less than or equivalent to hig
Nested Tables versus Index-by Tables The Index-by tables and nested tables are just similar. For e.g. They have similar structure and their individual elements are accessed in
Mutual Recursion The Subprograms are mutually recursive if they directly or indirectly call each other. In the illustration below, the Boolean functions odd & even, that dete
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