Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Existential Quantification - SQL
Existential quantification-stating that something is true of at least one object under consideration-can be expressed by OR(r,c), meaning that at least one object that satisfies a predicate for r also satisfies c, and IS_NOT_EMPTY(r). The names for the aggregate operators AND and OR reflect the facts that when we confine our attention to finite sets, universal and existential quantification are equivalent to repeated invocations of dyadic AND and dyadic OR, respectively. Note that AND(r,c) is equivalent to COUNT(r) = COUNT(r WHERE c), and OR(r,c) is equivalent to COUNT(r WHERE c) > 0 and also to IS_NOT_EMPTY(r WHERE c).
Quantification also appears in various guises in SQL, but its meaning is muddied by those same two violations of relational theory that we have already seen muddying the waters: duplicate rows and NULL. For example, SQL's (SELECT COUNT(*) FROM r), a so-called scalar subquery (because it is an expression denoting a table with one row and one column, enclosed in parentheses), denotes the number of rows in the table r, but can we really say that this represents the number of objects that satisfy a predicate for r, if the same row can be counted more than once, or if NULL appears in place of a column value in some row of r? In fact, what might it mean to say that a row does or does not satisfy a predicate? In 2VL we say that object a satisfies predicate P(x) exactly when P(a) is true. Does this still hold in 3VL, or might SQL deem a to satisfy P(x) also when P(a) is unknown? Well, it turns out that SQL uses both interpretations, depending on the context, as we shall discover.
Parameter and Keyword Description: table_reference: This keyword identifies the table or view that should be accessible when you execute the UPDATE statement, and for wh
Project Description: I am looking to change FullCalendar to add/delete sql server data when events are removed or dropped from Calendar. Events should only be included by dra
Operators on Tables and Rows Row Extraction TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column.
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
Parameter and Keyword Description: cursor_name: This identifies an explicit cursor formerly declared within the present scope. cursor_variable_name: These identif
%TYPE Attribute The %TYPE attribute gives the datatype of a record, field, nested table, database column, or the variable. You can use the %TYPE attribute as the datatype speci
Cursor Variables As Parameters You can declare the cursor variables as the formal parameters of the functions and procedures. In the illustration below, you define the REF CUR
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
Create the four tables and populate them with the given data. Answer the following queries in SQL. 1. Get all part-color/part-city combinations. Note: Here and subsequently, the
I want to implement heap sort algorithm in pl sql please share the source code for guidance
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd