Union all - sql, PL-SQL Programming

UNION ALL - SQL

Further varieties of UNION arise when we replace the key word DISTINCT by ALL in any of the foregoing examples, as in Example. ALL specifies that if row r appears n times in one operand and m times in the other, then it appears n+m times in the result-i.e., no elimination of duplicate rows takes place.

Example: UNION ALL

SELECT StudentId

FROM IS_CALLED

WHERE Name = 'Devinder'

UNION ALL

SELECT StudentId

FROM IS_ENROLLED_ON

WHERE CourseId = 'C1'

Clearly, UNION ALL represents another departure from relational theory. However, it is commonly used when the operands can be guaranteed to be disjoint because in such cases omission of ALL would incur the possibly significant overhead of the duplicate elimination process with no effect on the final result. Some authorities have argued that there really ought to be yet another variety of UNION, such that if row r appears n times in one operand and m times in the other, with m, n, then it appears m times in the result. Relational devotees might smile at this observation but refrain from comment.

Posted Date: 1/18/2013 5:37:00 AM | Location : United States







Related Discussions:- Union all - sql, Assignment Help, Ask Question on Union all - sql, Get Answer, Expert's Help, Union all - sql Discussions

Write discussion on Union all - sql
Your posts are moderated
Related Questions
Tautologies: Above given table allows us to read the truth of the connectives in the next manner. Just expect we are looking at row three. It means this says that, if there P

Comparison Operators Usually, you use the comparison operators in the WHERE clause of a data manipulation statement to form the predicates, that compare one expression to anot

Transaction Control The Oracle is transaction oriented; that is, Oracle uses the transactions to make sure the data integrity. The transaction is a sequence of SQL data manip

DBMS: The answer to this question is of course given in of the theory book. This book is concerned with SQL DBMSs and SQL databases in particular. Soon we will be looking a

Write a query to find academics that are authors and that have only ever coauthored papers with authors from institutes in the same state as their own. List their academic number,

Overriding Default Locking By default, the Oracle locks the data structures for you automatically. Though, you can request exact data locks on rows or tables when it is to you

i NEED THE QURIES TO SOME OF THE PROBLEMS USING plsql

SQL Functions The PL/SQL uses all the SQL functions involving the following aggregate functions that summarize the whole columns of the Oracle data: GROUPING, AVG, COUNT, STDDE

Recursion versus Iteration Dissimilar the iteration, recursion is not crucial to PL/SQL programming. Any problem which can be solved using recursion can be solving using the it

SELECT INTO Statement   The SELECT INTO statement retrieve data from one or more database tables, and then assigns the selected values to the variables or fields. Syntax: