Effects of null for unique specification - sql, PL-SQL Programming

Assignment Help:

Effects of NULL for UNIQUE Specification

When a UNIQUE specification u for base table t includes a column c that is not subject to a NOT NULL constraint, the appearance of several rows having NULL in place of a value for c and equal values for the other columns specified in u is permitted. It is only when each column of the specified "key" has a value that those column values may not appear in the same combination in more than one row of t.


Related Discussions:- Effects of null for unique specification - sql

Data types in sql - integer, Data Types in SQL - Integer INTEGER or  s...

Data Types in SQL - Integer INTEGER or  synonymously INT, for integers within a certain range. SQL additionally has types SMALLINT and BIGINT for certain ranges of integers. T

Application to export excel data to mssql server table, Application to Expo...

Application to Export Excel Data to MSSQL Server table I am having a table available in excel format and features the subsequent: - Some text is in Arabic (e.g. UTF-8 encodin

Operators on tables and rows, Operators on Tables and Rows Row Extrac...

Operators on Tables and Rows Row Extraction TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column.

Controlling cursor variables, Controlling Cursor Variables You use 3 s...

Controlling Cursor Variables You use 3 statements to control the cursor variable: OPEN-FOR, FETCH, & CLOSE. At First, you OPEN a cursor variable FOR a multi-row query. Then, y

Origin of earth - big bang hypothesis, ORIGIN OF EARTH - BIG-BAN G HY...

ORIGIN OF EARTH - BIG-BAN G HYPOTHESIS - Origin of life is linked to origin of earth. Cosmos, the Universe originated 10-20 billion years ago by Big Bang (thermonu

Product-specific packages in pl/sql, Product-specific Packages The Ora...

Product-specific Packages The Oracle and different Oracle tools are supplied with the product-specific packages which help you to build the PL/SQL-based applications. For illu

Use triggers to maintain referential integrity, At times, Brewbean's has ch...

At times, Brewbean's has changed the id number for existing products. In the past, they have had to add a new product row with the new id to the BB_PRODUCT table, modify all the co

Transaction context, Transaction context As the figure shows, the majo...

Transaction context As the figure shows, the major transaction shares its context with the nested transactions, but not with the autonomous transactions. Similarly, If one aut

Comparison operators- pl/sql, Comparison Operators The Comparison operat...

Comparison Operators The Comparison operators can compare one expression to another. The outcome is always true, false, or null. Usually, you use a comparison operators in condi

Passing cursor parameters, Passing Cursor Parameters You use the OPEN ...

Passing Cursor Parameters You use the OPEN statement to pass the parameters to a cursor. Unless you want to accept the default values, each proper parameter in the cursor decl

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