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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.
Control Structures The Control structures are the most important PL/SQL extension to the SQL. Not only does PL/SQL let you manipulate Oracle data, it lets you process the data
Overview of control structures According to the structure theorem, any computer program can be written by using the basic control structures as shown in figure below. They can b
Inserting Objects: You can use the INSERT statement to add objects to an object table. In the illustration below, you insert a Person object into the object table persons:
Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k
Effects of NULL for Multiple Assignments - SQL If the row expression given as the source for a multiple assignment evaluates to NULL, then NULL is assigned to each target. If
Semidifference via NOT IN and a subquery SELECT StudentId FROM IS_CALLED WHERE Name = 'Devinder' AND StudentId NOT IN (SELECT StudentId FROM IS_ENROLLED_ON WHER
DECLARE : This keyword signals the beginning of the declarative section of the PL/SQL block, that contains local declarations. The Items declared locally exist only within the
IN Mode An IN parameter pass the values to the subprogram being called. Within the subprogram, an IN parameter acts like a constant. And hence, it cannot be assigned a value.
Advantages of Exceptions Using the exceptions for the error handling has many benefits. Without an exception handling, every time you issue a command, you should ensure for th
Using Operator DEREF: You cannot navigate through refs within the PL/SQL procedural statements. Rather than, you should use the operator DEREF in the SQL statement. The DEREF
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