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
Using EXTEND To enlarge the size of a collection, use EXTEND. This process has 3 forms. The EXTEND appends one null element to a collection. And the EXTEND(n) appends n null e

Example of Tables within a Table - SQL Example: Obtaining C_ER from COURSE and EXAM_MARK SELECT CourseId, CAST (TABLE (SELECT DISTINCT StudentId, Mark FROM EXAM_MARK AS EM

Use of COUNT in SQL It describes and discusses various general methods of expressing constraints, eventually noting that support for "=" with relation operands is sufficient f

BETWEEN and NOT BETWEEN Operator in SQL Example: Restricting exam marks to between 0 and 100 CREATE ASSERTION Marks_between_0_and_100 CHECK (NOT EXISTS (SELECT * FROM

COSMOZOI C THEORY - Richter (1865) proposed the cosmozoic theory that says that life came by spores (cosmozoa) or other particles from other planets on the earth.

%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche

Data Types in SQL - Integer INTEGER or  synonymously INT, for integers within a certain range. SQL additionally has types SMALLINT and BIGINT for certain ranges of integers. T

Parameter and Keyword Description:   table_reference: This identifies a table or view which should be available when you execute the INSERT statement, and for that you sho

Iteration Schemes The bounds of a loop range can be variables, literals, variables, or expressions but must compute to integers. Below are some of the examples. As you can see t

Expressions   An expression is a randomly complex combination of the constants, variables, literals, operators, & function calls. The simplest expression is the single variabl