Effects of null for unique specification

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

Recursion, Recursion The Recursion is a powerful method for simplify th...

Recursion The Recursion is a powerful method for simplify the design of the algorithms. Principally, the recursion means the self-reference. In the recursive mathematical serie

Using a host variable, Using a Host Variable You can declare the curso...

Using a Host Variable You can declare the cursor variable in the PL/SQL host environment like an OCI or Pro C program. To use the cursor variable, you should pass it as a host

Sql, Write a cursor to open an employee database and fetch the employee rec...

Write a cursor to open an employee database and fetch the employee record whose age is greater than 45

Calculate the total shopper spending, Many of the reports generated from th...

Many of the reports generated from the system calculate the total dollars in purchases for a shopper. Complete the following steps to create a function named TOT_PURCH_SF that acce

Updating by insertion, Updating by insertion Syntax : INSERT IN...

Updating by insertion Syntax : INSERT INTO ENROLMENT VALUES (SID ('S4'), 'Devinder', CID ('C1'));

Insert statement - syntax, INSERT Statement The INSERT statement adds f...

INSERT Statement The INSERT statement adds fresh rows of data to the specified database table or view. Syntax:

Packaging cursors, Packaging Cursors You can split a cursor specific...

Packaging Cursors You can split a cursor specification from its body for placement in a package. In that way, you can change the cursor body without changing the cursor spec

Features of pl/sql, Main features of PL/SQL A good way to get familiar ...

Main features of PL/SQL A good way to get familiar with PL/SQL is to look at a sample program. The below program processes an order for tennis rackets. At first, it declares a

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

Package body, The Package Body The package specification is implemented...

The Package Body The package specification is implemented by the package body. That is, the package body has the definition of every cursor and the subprogram declared in the p

Write Your Message!

Name

Email id

Message

Verfication Code

User Account

All Pages