Creating a table, PL-SQL Programming

Creating a Table

Syantax:

CREATE TABLE ENROLMENT

(StudentId SID,

Name   VARCHAR (30) NOT NULL,

CourseId CID,

PRIMARY KEY (StudentId, CourseId)) ;

Explanation:

  1. CREATE TABLE ENROLMENT announces that what follows defines a variable in the database, named ENROLMENT. A variable in an SQL database is necessarily a table variable, just as in a relational database every variable is a relation variable. SQL does not use the term variable, instead referring to the variable as a base table (its value being called a table, of course).
  2. StudentId SID defines the first column of ENROLMENT, giving its name and either its declared type (a user-defined type) or its domain-we cannot tell which. If SID is a domain, then the definition of that domain specifies the declared type of the column StudentId. Similarly, Name VARCHAR(30) and CourseId CID define the second and third columns of ENROLMENT, respectively. A system-defined type is explicitly given for the column Name but the remarks on the declared type of StudentId apply in similar fashion to CourseId. Note carefully that in SQL it is correct, in ordinary prose, to identify columns by their ordinal position. By contrast there is no such thing as "the first attribute" of a relation or a relation variable.
  3. NOT NULL, appended to the definition of Name, specifies a constraint to the effect that the table assigned to ENROLMENT cannot contain a row in which "the null value of type VARCHAR(30)" appears for that column. The constraint is needed for accurate emulation of Example 2.6 in the theory book because relational theory does not admit any counterpart of SQL's NULL (so nor does Tutorial D). See the next bullet for an explanation of why NOT NULL is not appended to the other two column definitions.
  4. PRIMARY KEY ( StudentId, CourseId ) specifies that at no time can two distinct rows appear in the current value of ENROLMENT having the same value for StudentId and also the same value for CourseId. In enterprise terms, no two enrolments can involve the same student and the same course. In addition, it implies that the NOT NULL constraint applies to each those two columns.
Posted Date: 1/18/2013 2:46:47 AM | Location : United States







Related Discussions:- Creating a table, Assignment Help, Ask Question on Creating a table, Get Answer, Expert's Help, Creating a table Discussions

Write discussion on Creating a table
Your posts are moderated
Related Questions
Difference between 9i & 10G When Oracle releases any new databases then it are having some discrepancy with them. But 10G is having much difference than oracle 9i has. Oracle

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

Quantification in SQL To quantify something, as the theory book has it, is to state its quantity, to say how many of it there are. For example, in Tutorial D the expression CO

Cause of Indeterminacy in SQL One root cause of indeterminacy in SQL lies in its implementation of comparison for equality. For certain system-defined types it is possible for

%ROWCOUNT The %ROWCOUNT yields the number of rows affected by the INSERT, UPDATE, or DELETE statement, or returned by a SELECT INTO statement. The %ROWCOUNT yields zero when a

Create a procedure named STATUS_SHIP_SP that allows a company to employee in the Shipping Department to update the status of an order to add shipping information. The BB_BASKETSTAT

Attributes: Just similar to variable, an attribute is declared with a name and datatype. The name should be exclusive within the object type. The datatype can be any Oracle ty

Magento change address format depending on store Project Description: What I need is that depending on the store in which the customer bought the address should change the fo

FORALL Statement The FORALL statements instruct the PL/SQL engine to bulk-bind the input collections before sending them to the SQL engine. Though the FORALL statement consists

Assignment Statement: The assignment statement sets the present value of the variable, parameter, field, or element. The statement consists of an assignment target followed by