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!
Closest Approximation to Relational Union - SQL
Actually, just as SQL has several varieties of JOIN, it also has several varieties of UNION, none of which is equivalent to the relational operator of that name. The closest approximation to relational union is illustrated in Example.
Example: SQL's closest approximation to relational union
SELECT StudentId
FROM IS_CALLED
WHERE Name = 'Devinder'
UNION DISTINCT CORRESPONDING
FROM IS_ENROLLED_ON
WHERE CourseId = 'C1'
The key word DISTINCT is optional and implied by default (somewhat curiously so, considering that its opposite, ALL, is the default option in the SELECT clause). It specifies that no row is to appear more than once in the result. Thus, there is never a need to include DISTINCT in either of the SELECT clauses, and this would be the case even if the WHERE clause were omitted from the specification of the second operand in Example, allowing the same StudentId value to appear more than once in that operand.
The key word CORRESPONDING specifies that operand columns are to be paired by name, just as in relational union.
Boolean Values Only the values TRUE, FALSE, & NULL can be assigned to a Boolean variable. For illustration, given the declaration DECLARE done BOOLEAN; the following statements
Other monadic - SQL In 2VL there are just 4 (2 2 ) monadic operators, of which negation is really the only "useful" one. When a third truth value is introduced we have 27 (3 3
Table Literals - SQL One might expect SQL to support table literals in the manner illustrated in Example 2.2, but in fact that is not a legal SQL expression. Example: Not a
FETCH Statement The FETCH statement retrieve rows of data one at a time from the result set of the multi-row query. The data is stored in fields or variables which correspond t
Effects of NULL The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL
Example of UNWRAP Operator - SQL Example here shows how unwrapping can be done in longhand in SQL. Example: Unwrapping in SQL Letting CONTACT_INFO_WRAPPED denote the res
IS NULL Operator The IS NULL operator returns the Boolean value TRUE whenever its operand is null or FALSE if it is not null. The comparisons including the nulls always yield NU
Overloading: Similar to packaged subprograms, methods of the same type can be overloaded. That is, you can use similar name for various methods if their formal parameters diff
BEGIN Parameter Description in pl sql: BEGIN: This keyword signals the beginning of the executable section of a PL/SQL block, that contains executable statements. The execut
How Calls Are Resolved? The figure shows that how the PL/SQL compiler resolves the subprogram calls. When the compiler encounters the procedure or function call, it tries to di
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