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Declarations in SQLYour program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot. You can declare the variables and constants in the declarative part of any PL/SQL block, package, or subprogram. The Declarations allocate the storage space for a value, state its datatype, and name the storage location and hence, you can reference it. A couple of examples are shown below: birthday DATE;emp_count SMALLINT := 0;The first declaration names a variable of the type DATE. The second declaration names a variable of the type SMALLINT and uses the assignment operator to assign an initial value of zero to the variable. The example next show that the expression following the assignment operator can be arbitrarily complex and can refer to the earlier initialized variables: pi REAL := 3.14159;radius REAL := 1;area REAL := pi * radius**2; By default, the variables are initialized to NULL. So, these declarations are equal: birthday DATE;birthday DATE := NULL; In the declaration of a constant, the keyword CONSTANT should precede the type of the specifier, as the example below shows: credit_limit CONSTANT REAL := 5000.00; This declaration names a constant of the type REAL and assigns an initial value of 5000 to the constant. The constant must be initialized in its declaration. Or else, you get a compilation error whenever the declaration is elaborated. (The procedure of a declaration by the PL/SQL compiler is known as the elaboration.)
Error Handling The PL/SQL makes it easy to detect and process the predefined and user-defined error conditions known as exceptions. Whenever an error occurs, an exception is ra
Logical Operators The logical operators AND, NOT, and OR follow the tri-state logic shown in table below. The AND and OR are binary operators; NOT is a unary operator.
Conditionals - SQL At first sight SQL does not appear to have a single operator for expressing logical implication. In this respect it would be in common with most programming
At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean's wants to create a trigger that automatically updates the stock level of all pr
Using the student and faculty tables create a select query that outputs all students for a specific advisor. Generate the execution plan, select out the explain plan . Create an
Declaring Exceptions The Exceptions can be declared only in the declarative part of the PL/SQL subprogram, block, or package. By introducing its name, you can declare an excep
Data Abstraction The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to reme
SELECT INTO Statement The SELECT INTO statement retrieve data from one or more database tables, and then assigns the selected values to the variables or fields. Syntax:
Name Resolution In potentially uncertain SQL statements, the names of the database columns take precedence over the names of the local variables and formal parameters. For e.g.
Obtaining a natural join by specifying the common columns Synatax: SELECT * FROM IS_CALLED JOIN IS_ENROLLED_ON USING ( StudentId ) However, a named columns join doe
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