Union and or - sql, PL-SQL Programming

Assignment Help:

UNION and OR - SQL

SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, such that IS_CALLED NATURAL JOIN IS_ENROLLED_ON, for example, can be an element of that clause but cannot stand alone as a table expression. Instead, UNION always connects table expressions that can stand alone, these being:

  1. SELECT expressions
  2. TABLE tn, which is equivalent to SELECT * FROM tn, where tn is a table name
  3. VALUES expressions
  4. Invocations of UNION, INTERSECT and EXCEPT

Related Discussions:- Union and or - sql

How transactions guard your database, How Transactions Guard Your Database ...

How Transactions Guard Your Database The transaction is a sequence of SQL data manipulation statements which does a logical unit of work. The Oracle treats the sequence of SQL

Autonomous versus nested transactions, Autonomous versus Nested Transaction...

Autonomous versus Nested Transactions Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below: (i)

Boolean values-assignments in pl/sql, Boolean Values Only the values TRU...

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

Remote operations in pl sql, Remote Operations: As the illustration sh...

Remote Operations: As the illustration shows below, the PL/SQL subprograms can execute the dynamic SQL statements which refer to the objects on a remote database: PROCEDURE

Example of add constraint in sql, Example of ADD CONSTRAINT in SQL Exa...

Example of ADD CONSTRAINT in SQL Example: Alternative formulation for MAX_ENROLMENTS ALTER TABLE IS_ENROLLED_ON ADD CONSTRAINT MAX_ENROLMENTS CHECK ((SELECT COUNT (*)

Declaring exceptions - user-defined exceptions, Declaring Exceptions T...

Declaring Exceptions The Exceptions can be declared only in the declarative part of the PL/SQL subprogram, block, or package. By introducing its name, you can declare an excep

Constants and variables in pl sql, Constants and Variables:   You can...

Constants and Variables:   You can declare the constants and variables in the declarative section of any PL/SQL subprogram, block, or package. The Declarations allot the stor

Example of foreign key constraint - sql, Example of Foreign Key Constraint ...

Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam

Effect of anonymous columns, Effect of Anonymous Columns Now, recall t...

Effect of Anonymous Columns Now, recall that a VALUES expression denotes a table with undefined column names. If an initial value is to be specified when a base table is creat

Natural join - sql, Natural Join - SQL In the absence of NATURAL JOIN...

Natural Join - SQL In the absence of NATURAL JOIN Example has to be replaced by something rather more longwinded, as shown in Example. Example: Joining IS_CALLED and IS_EN

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

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!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd