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
Data Types in SQL - Decimal DECIMAL, NUMERIC, REAL, FLOAT and various other terms for various sets of rational numbers. When these key words are specified for the declared typ

Data Types in SQL - Timestamp TIMESTAMP for values representing points in time on a specified uniform scale. DATE is used for timestamps on a scale of one day, such as DATE '2

Explicit Cursor Attributes The cursor variable or each cursor has four attributes: %FOUND, %ISOPEN, %ROWCOUNT, and %NOTFOUND. When appended to the cursor or cursor variable, th

Using a join on 2 tables, select all columns and 10 rows from the 2 tables without the use of a Cartesian product. Query: SELECT * FROM EMPLOYEE1 E JOIN STAFF S ON E.EMP_

The accuracy of product table data is critical and the Brwebean's. owner wants to have an audit file that contains information regarding all DML activity on the BB_PRODUCT table. T

Consider the schema for FreeChecking Bank, that we designed given below. Translate the given ER schema into SQL CREATE TABLE statements (indicating primary key, unique and foreign

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 Exceptions Using the exceptions for the error handling has many benefits. Without an exception handling, every time you issue a command, you should ensure for th

Assignments in pl/sql The Variables and constants are initialized every time a block or subprogram is entered. By default, the variables are initialized to NULL. Therefore, unle

Effects of NULL in Aggregate Operator - SQL Let aggop(x) be an invocation of some aggregate operator aggop in SQL, where x is an expression (usually an open expression) to be