Keys in sql, PL-SQL Programming

Keys in SQL

SQL support for keys in the following respects:

  1. SQL does not require at least one key for every base table. If no key is explicitly declared, then KEY {ALL BUT} is implicit.
  2. When no key is specified there is no prohibition on multiple appearances of the same row.
  3. SQL does not recognize the empty set as a key.
  4. SQL allows a key to be a proper superset of another key for the same base table. (This "feature" is sometimes used as a workaround for the fact that the columns of the foreign key are required to correspond to those of a declared key of the referenced table.)
Posted Date: 1/18/2013 11:31:39 PM | Location : United States







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

Write discussion on Keys in sql
Your posts are moderated
Related Questions
DELETE Command - SQL Loosely speaking, DELETE removes some existing rows from its target table. Suppose the university decides that course C3 is to be withdrawn. Example shows

Data Types in SQL - Interval, Boolean INTERVAL for values denoting, not intervals (!) but durations in time, such as 5 years, 3 days, 2 minutes, and so on. BOOLEAN, con

Multiple Assignment- SQL SQL supports multiple assignment to local variables and also applies multiple assignment semantics in SET clauses of UPDATE statements, but does not

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

Updating Variables For assignment, SQL uses the key word SET, as in SET X = X + 1 (read as "set X equal to X+1") rather than X: = X + 1 as found in many computer languages.

TTITLE and BTITLE are commands in Pl-SQL to control report headings and footers. This Ttitle & Btitle are mainly used on creating SQL*PLUS report. Ttitle is used for toptitle headi

Role of Abstraction in pl/sql: The abstraction is a high-level description or model of a real-world entity. The Abstractions keep our daily lives convenient. They help us ca

Restriction in SQL Syntax: SELECT DISTINCT StudentId FROM IS_CALLED WHERE Name = 'Boris' The WHERE clause operates on the result of the FROM clause in analogo

Advantages of Invoker Rights The Invoker-rights routines centralize the data retrieval. They are particularly helpful in applications which store data in various schemas. In su

Substitution and Instantiation - SQL It shows how NULL might appear in substitution for a parameter of a predicate and how it might thus participate in instantiation of that p