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

First step at defining type sid in sql, First Step at defining type SID in ...

First Step at defining type SID in SQL CREATE TYPE SID AS ( C VARCHAR(5) ) ; Explanation: TYPE SID announces that a type named SID is being defined to the syst

Opening a cursor variable, Opening a Cursor Variable The OPEN-FOR stat...

Opening a Cursor Variable The OPEN-FOR statement relates a cursor variable with the multi-row query, executes the query, and then identifies the result set. The syntax for ope

Update statement - syntax, UPDATE Statement The UPDATE statement tra...

UPDATE Statement The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:

Inner join, Inner Join We have learned how to retrieve data from one t...

Inner Join We have learned how to retrieve data from one table by using SELECT statement. But, as we have learned, normalized relational databases mean the data is spread betw

Using set transaction, Using SET TRANSACTION You use the SET TRANSACTI...

Using SET TRANSACTION You use the SET TRANSACTION statement to begin the read-only or read-write transaction, start an isolation level, or assign your present transaction to a

Advantages of subprograms, Advantages of Subprograms The Subprograms g...

Advantages of Subprograms The Subprograms give extensibility; that is, tailor the PL/SQL language to suit your requirements. For illustration, if you require a procedure which

Sql script to create and populate the tables, Create the four tables and po...

Create the four tables and populate them with the given data. Answer the following queries in SQL. 1. Get all part-color/part-city combinations. Note: Here and subsequently, the

Character types in pl/sql, Character Types The Character types allow yo...

Character Types The Character types allow you to store alphanumeric data, represent words and text, and manipulate the character strings. CHAR You use the CHAR dataty

Effects of null for union - sql, Effects of NULL for union - SQL The ...

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 compari

Using aggregation on nested tables - sql, Using Aggregation on Nested Table...

Using Aggregation on Nested Tables Example is the most direct translation of its counterpart in the theory book that can be obtained in SQL but it is so over-elaborate that no

Write Your Message!

Name

Email id

Message

Verfication Code

User Account

All Pages