Third step at defining type sid in sql, PL-SQL Programming

Assignment Help:

Third Step at defining type SID in SQL

CREATE DOMAIN SID AS VARCHAR(5)

CHECK ( VALUE IS NOT NULL AND

SUBSTRING(VALUE FROM 1 FOR 1) = 'S' AND

CAST('+'||SUBSTRING(VALUE FROM 2) AS INTEGER) >= 0 );

Explanation:

DOMAIN SID announces that a domain named SID is being defined to the system.
AS VARCHAR(5) specifies that values in domain SID are certain values of type VARCHAR(5).
CHECK ( ... ) specifies a constraint defining exactly which values of type VARCHAR(5) are in the domain SID. Note that the key word VALUE, which is available only in domain constraints, refers (in this particular example) to an arbitrary value of type VARCHAR(5).
VALUE IS NOT NULL specifies that the null value of type VARCHAR(5) is not a value in the domain. This is needed because the other conjuncts evaluate to UNKNOWN if VALUE is the null value and a domain constraint is deemed to be violated only when it evaluates to FALSE.
SUBSTRING(VALUE FROM 1 FOR 1) = 'S' specifies that every value in the domain must begin with S. Note SQL's deliberate use of "noise" words in the invocation of SUBSTRING, the justification for which is to distinguish invocations of system-defined operators from those of user-defined ones.
CAST('+'||SUBSTRING(VALUE FROM 2) AS INTEGER) >= 0 is an attempt to emulate an invocation of IS_DIGITS, perhaps showing how a user-defined operator of that name might be implemented in SQL. The character "+" is concatenated to the putatively numeric portion of the string in order to exclude values such as 'S+123' from the domain (the string '+123' can be cast as an integer but '++123' cannot).

Related Discussions:- Third step at defining type sid in sql

Parameter and keyword description - fetch statement, Parameter and Keyword ...

Parameter and Keyword Description: cursor_name: This identifies an explicit cursor formerly declared within the present scope. cursor_variable_name: These identif

Sequential control - pl/sql, Sequential Control Dissimilar to the IF and ...

Sequential Control Dissimilar to the IF and LOOP statements, the GOTO and NULL statements are not important to the PL/SQL programming. The configuration of PL/SQL is such that th

Difference between implicit and explicit cursor, Implicit Cursor is declare...

Implicit Cursor is declared and used by the oracle environment internally. while the explicit cursor is declared and used by the external user. more over implicitly cursors are no

While-loop - iterative control, WHILE-LOOP The WHILE-LOOP statement rela...

WHILE-LOOP The WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown: WHILE condition LOOP sequence_of_sta

Need for dynamic sql - pl sql , Need for Dynamic SQL: You need dynamic...

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

Expression in assignment statement - pl sql, Expression: This is a ran...

Expression: This is a randomly complex combination of constants, variables, literals, operators, & function calls. The simplest expression consists of a single variable. If th

Table represents an extension - sql, Table Represents an Extension - SQL ...

Table Represents an Extension - SQL It describes how each tuple in a relation represents a true instantiation of some predicate and each true instantiation is represented by s

Calling constructors in pl sql, Calling Constructors: The Calls to a c...

Calling Constructors: The Calls to a constructor are allowed wherever the function calls are allowed. Similarly to the functions, a constructor is called as a section of an ex

Read-only operator (+) - sql, Read-Only Operator (+) - SQL The term r...

Read-Only Operator (+) - SQL The term read-only operator to the mathematical term function. Here I just need to add that the SQL standard reserves the term function for read-

Entering and exiting - autonomous transaction, Entering and Exiting If...

Entering and Exiting If you enter the executable part of an autonomous routine, the major transaction suspends. When you exit the routine, the major transaction resumes. To ex

Write Your Message!

Name

Email id

Message

Verfication Code

User Account

All Pages