Effects of null for union - sql, PL-SQL Programming

Assignment Help:

Effects of NULL for union - SQL

The treatment of NULL in invocations of EXCEPT is as for UNION. This is different from its treatment in those of NOT IN and quantified comparisons. In the case of t1 EXCEPT t2, row r of t1 appears in the result if and only if there does not exist a row s in t2 such that r IS NOT DISTINCT FROM s evaluates to TRUE. Note that x NOT IN (t) evaluates to UNKNOWN whenever x = x does, including in particular the case where x IS NULL evaluates to TRUE because every field of the row x is the null value. Recall that when the condition given in a WHERE clause evaluates to UNKNOWN for row r, then r does not appear in the result.


Related Discussions:- Effects of null for union - sql

Group and having query, Using a join on 2 tables, select all columns and 10...

Using a join on 2 tables, select all columns and 10 rows from the 2 tables without the use of a Cartesian product. Query: SELECT * FROM EMPLOYEE1 E JOIN STAFF S ON E.EMP_

Query optimization, 1.( /5 marks) Suppose that a B+-tree index with the sea...

1.( /5 marks) Suppose that a B+-tree index with the search key (dept_name, building) is available on relation department. What would be the best way to handle the following selecti

Running the pl/sql wrapper, Running the PL/SQL Wrapper To run the PL/SQ...

Running the PL/SQL Wrapper To run the PL/SQL Wrapper, go through the wrap command at your operating system prompt by using the syntax as shown: wrap iname=input_file [oname=

Aggregate operators sql, Aggregate Operators SQL Supports all of the a...

Aggregate Operators SQL Supports all of the aggregate operators mentioned in the theory book and many more besides. The syntax, however, involves an unusual trick that SQL cal

Loop labels- iterative control, Loop Labels Like the PL/SQL blocks, loop...

Loop Labels Like the PL/SQL blocks, loops can also be labeled. The label, an undeclared identifier enclosed by double angle brackets, should appear at the beginning of the LOOP

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

Cursors, What is Cursors how to use it in Real time application ?

What is Cursors how to use it in Real time application ?

Using inner join, Using INNER JOIN INNER JOIN is used to retrieve the ...

Using INNER JOIN INNER JOIN is used to retrieve the data from all tables listed based on a condition of equality listed after keyword ON. If the condition is not meet, rows ar

Methods in pl/sql, Methods: In normal, a method is a subprogram declar...

Methods: In normal, a method is a subprogram declared in an object type specification using the keyword MEMBER or STATIC. The method cannot have similar name as the object typ

Advantages of packages, Advantages of Packages The benefits of the Pack...

Advantages of Packages The benefits of the Packages are as shown below: Modularity The Packages encapsulate logically associated items, types, and subprograms in the

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