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
Logical Operators The logical operators AND, NOT, and OR follow the tri-state logic shown in table below. The AND and OR are binary operators; NOT is a unary operator.

FORALL Statement The FORALL statements instruct the PL/SQL engine to bulk-bind the input collections before sending them to the SQL engine. Though the FORALL statement consists

Project Description: I have two types of data sources. One that is a list in SharePoint and another that is an access desktop database. The access desktop database is fairly com

Using a Join on 2 tables, select all columns and all rows from the tables without the use of a Cartesian product. Query: SELECT * FROM EMPLOYEE1 JOIN CONTRACT ON EMPLOYEE

Great Plains (Microsoft Dynamics) Purchases Report Project Description: I want to build a purchases report that matches the General Ledger. presently, when I join the PM20

Variable Declaration - SQL SQL's support for variables is very similar to Tutorial D's, except that the syntax for creating persistent  variables-base tables-is quite differen

Using FOR UPDATE If you declare a cursor which will be referenced in the CURRENT OF clause of an UPDATE or DELETE statement, you should use the FOR UPDATE clause to obtain an

Committing and Rolling Back The COMMIT and ROLLBACK end the active autonomous transaction but do not exit the autonomous routine. As the figure shows, if one transaction ends,

%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche

Using ROLLBACK The ROLLBACK statements end the present transaction and undo any change made during the transaction. The Rolling back is helpful for two reasons. Firstly, if yo