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.
#quesWrite a cursor to open an employee database and fetch the employee record whose age is greater than 45.tion..
Using Cursor Attributes: Every cursor has 4 attributes: %NOTFOUND, %FOUND, %ISOPEN, and %ROWCOUNT. If appended to the cursor name, they return the helpful information about
I want to implement heap sort algorithm in pl sql please share the source code for guidance
Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system
Using RENAME in combination with JOIN - SQL Example gives pairs of ids of students having the same name, by joining two renamings of IS_CALLED. Example gives an equivalent ex
Data Types in SQL - Decimal DECIMAL, NUMERIC, REAL, FLOAT and various other terms for various sets of rational numbers. When these key words are specified for the declared typ
Block Structure The PL/SQL is a block-structured language. That is, the fundamental units (procedures, anonymous blocks, and functions) that make up a PL/SQL program are logi
Using a join on 3 tables, select 5 columns and 10 rows from the 3 tables without the use of a Cartesian product Query: SELECT E.LAST_NAME, E.FIRST_NAME, S.BUILDING, S.BRAN
Object Type: The object type is a user-defined composite datatype which encapsulates a data structure along with the functions and procedures required to manipulate the data
Semidifference via EXCEPT and JOIN - SQL SELECT * FROM (SELECT StudentId FROM IS_CALLED WHERE Name = 'Devinder' EXCEPT DISTINCT CORRESPONDING SELECT StudentId
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