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

Parameter and keyword description - %type attribute, Parameter and Keyword ...

Parameter and Keyword Description: collection_name: This keyword identifies the index-by table, nested table, or varray formerly declared within the present scope. cu

Truth tables , Truth Tables: However in propositional logic - here we ...

Truth Tables: However in propositional logic - here we are restricted to expressing sentences and where the propositions are true or false - so we can check where a particular

Compare sql and pl/sql, Question 1 . Compare SQL and PL/SQL Question 2 ...

Question 1 . Compare SQL and PL/SQL Question 2 . Write a database trigger to implement the following check condition                          Given the following table

Definition of cross join - sql, Definition of CROSS JOIN - SQL Let s ...

Definition of CROSS JOIN - SQL Let s = t1 CROSS JOIN t2, where t1 and t2 are table expressions optionally accompanied by range variables. Then: Note: Here T denotes Table

Collections in pl sql, Collections:   The collection is an ordered gr...

Collections:   The collection is an ordered group of elements, all of similar type (for illustration, the grades for a class of students). Each element has an exclusive subsc

"not enforced" table constraints - sql, "Not Enforced" Table Constraints ...

"Not Enforced" Table Constraints A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to b

Using lock table, Using LOCK TABLE You use the LOCK TABLE statement to...

Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati

Parameter and keyword description - open-for statement, Parameter and Keywo...

Parameter and Keyword Description: cursor_variable_name: This identifies a cursor variable or the parameter formerly declared within the present scope. host_cursor_va

How bulk bind helps improvement in performance?, How Bulk Binds Improve Per...

How Bulk Binds Improve Performance The assigning of values to the PL/SQL variables in SQL statements is known as binding. The binding of the whole collection at once is know

Authorize and fetch data from instagram, Authorize and fetch data from Inst...

Authorize and fetch data from Instagram Project Description: Incorporate Instagram feed on mobile site platform: c#, ms sql, jquerymobile, jquery Web admin Author

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