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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.)
Use of Table Expressions - Expressing Constraint Conditions With the exception of key constraints, the examples in the theory book all explicitly reference at least one relvar
Special cases of projection This section describes the identity projection, r {ALL BUT}, and the projection on no attributes, r { }, which yields TABLE_DUM when r is empty, ot
UNION and OR - SQL SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, su
%ISOPEN The %ISOPEN yields TRUE if its cursor or cursor variable is open; or else, the %ISOPEN yields FALSE. In the illustration, you use the %ISOPEN to select an action:
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 (
Scope and Visibility The References to an identifier are resolved according to its visibility and scope. The scope of an identifier is that area of a program unit (subprogram, b
to write a heap sort program usin pl-sql
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
TTITLE and BTITLE are commands in Pl-SQL to control report headings and footers. This Ttitle & Btitle are mainly used on creating SQL*PLUS report. Ttitle is used for toptitle headi
FOR-LOOP While the number of iterations through a WHILE loop is unknown till the loop completes, then the number of iterations through a FOR loop is known before the loop is ent
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