Creating a table, PL-SQL Programming

Assignment Help:

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.

Related Discussions:- Creating a table

Package specification, The Package Specification The package specificat...

The Package Specification The package specifications contain the public declarations. The scopes of these declarations are local to your database representation and global to t

I need sql - wp sql expert, I need SQL , WP SQL Expert Project Descripti...

I need SQL , WP SQL Expert Project Description: Expert required to modify WP SQL query. Skills required are MySQL, SQL, PHP, Wordpress

How exceptions propagate in pl/sql programming?, How Exceptions Propagate ?...

How Exceptions Propagate ? Whenever an exception is raised, and if the PL/SQL cannot find a handler for it in the present subprogram or block, the exception propagates. That is

Using set transaction, Using SET TRANSACTION You use the SET TRANSACTI...

Using SET TRANSACTION You use the SET TRANSACTION statement to begin the read-only or read-write transaction, start an isolation level, or assign your present transaction to a

Exceptions are raised - Using Raise statement, How Exceptions Are Raised ...

How Exceptions Are Raised By the run-time system, the internal exceptions are raised implicitly as are user-defined exceptions that you have related with an Oracle error number

Keyword, what is the use of declare keyword

what is the use of declare keyword

Using for update, Using FOR UPDATE If you declare a cursor which will ...

Using FOR UPDATE If you declare a cursor which will be referenced in the CURRENT OF clause of an UPDATE or DELETE statement, you should use the FOR UPDATE clause to obtain an

Closing a cursor variable, Closing a Cursor Variable The CLOSE stateme...

Closing a Cursor Variable The CLOSE statement disables the cursor variable. After that, the related result set is undefined. The syntax for the same is as shown below: CLOS

Use native dynamic sql - improve performance of application, Use Native Dyn...

Use Native Dynamic SQL A few programs (a normal-purpose report writer for illustration) should build and process a variety of SQL statements at run time. Therefore, their full

I need sql to infopath data connection, I need SQL to infopath data connect...

I need SQL to infopath data connection Project Description: Want data retrieval connection from SQL to SharePoint infopath Skills required are Sharepoint, SQL

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd