Example of not exists operator - sql, PL-SQL Programming

Assignment Help:

Example of NOT EXISTS Operator - SQL

Example is a translation into SQL of the corresponding example, which is included there merely to show that for any scalar comparison there is an alternative formulation using IS_EMPTY.

Example: MAX_ENROLMENTS expressed using an invocation of NOT EXISTS

CREATE ASSERTION MAX_ENROLMENTS_alternative1

CHECK (NOT EXISTS (SELECT *

FROM (VALUES (SELECT COUNT (*)

FROM IS_ENROLLED_ON)) AS

V (N)

WHERE V.N > 20000));

Explanation

VALUES ( SELECT COUNT(*) FROM IS_ENROLLED_ON ) denotes a table with just one column, unnamed, in whose single row the value of that column is the number of rows in the current value of IS_ENROLLED_ON. The SELECT expression is parenthesized to make it into a scalar subquery and given as the argument to an invocation of VALUES, which makes the number denoted by that scalar subquery into a one-row, one-column table. (Actually, it might be safer to place an extra pair of parentheses around the SELECT expression here. Although VALUES 1 and VALUES (1) are equivalent, it might not be clear as to which role the single parentheses are taking: do they denote a scalar subquery, as I have assumed, or are they the optional ones surrounding a single table expression? If the latter, we would expect a syntax error.)
AS V (N) defines the range variable V to refer to what in this case is just the single row of that table, and also assigns the name N to its only column.
WHERE V.N > 20000 operates on that one-row, one-column table to yield a table of heading (N INTEGER) that is empty if and only if the single row in that one-row, one-column table fails to satisfy the condition N > 20000. Thus, the result is empty only when the number of enrolments is in fact no greater than the maximum allowed.

Related Discussions:- Example of not exists operator - sql

Aggregate assignment-declarations in sql, Aggregate Assignment The %ROWT...

Aggregate Assignment The %ROWTYPE declaration cannot include an initialization clause. Though, there are two ways to assign values to all fields in a record at once. At First, t

Using delete - collection method, Using DELETE This process has three ...

Using DELETE This process has three forms. The DELETE removes all elements from the collection. DELETE(n) removes the nth element from the nested table. When n is null, then D

Example of coalesce operator - sql, Example of COALESCE operator Examp...

Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM

Manipulating objects in pl sql, Manipulating Objects: You can use an o...

Manipulating Objects: You can use an object type in the CREATE TABLE statement to indicate the datatype of a column. When the table is created once, you can use the SQL statem

Write an anonymous block that contains a pl/sql function, a. Write an anon...

a. Write an anonymous block that contains a PL/SQL function. Given an order number orderNo, the function will calculate the total number of the parts in the order. Then the anonym

Set operators - sql operators, Set Operators The Set operators combine...

Set Operators The Set operators combine the results of the two queries into one result. The INTERSECT returns all the distinct rows selected by both queries. The MINUS returns

Updating a variable, Updating a Variable Assignment of an attribute va...

Updating a Variable Assignment of an attribute value in a variable of a structured type Synatx: SET SN.C = 'S2'; As in Example the entire statement is equivalent to a

Create a procedure that update the status, Create a procedure named STATUS_...

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

Implicit cursor attributes, Implicit Cursor Attributes The Implicit cur...

Implicit Cursor Attributes The Implicit cursor attributes returns the information about the execution of an INSERT, DELETE, UPDATE, or SELECT INTO statement. The cursor attribu

Accessing attributes in pl sql, Accessing Attributes: You can refer to ...

Accessing Attributes: You can refer to an attribute only by its name not by its position in the object type. To access or modify the value of an attribute, you can use the dot

Write Your Message!

Name

Email id

Message

Verfication Code

User Account

All Pages