Relational Algebra - SQL

It describes some operators, that together constitute an algebra that is not only relationally complete but also irreducibly so (very nearly- apart from RENAME, which can be expressed in terms of extension and projection, none of those operators can be discarded without sacrificing completeness). We can use these operators as a basis for testing SQL for relational completeness. If we can show that for every invocation of one of these operators there is an equivalent SQL expression, then we will have shown that SQL is relationally complete. By "equivalent" we mean an expression whose table operands are counterparts of the relation operands (ignoring the ordering that SQL imposes on the columns) and whose result is a table counterpart result, where a table is a counterpart of a relation if and only if it satisfies all of the following conditions:

• Every column has a name
• No two distinct columns have the same name
• No row appears more than once
• Null doesn't appear in place of a value anywhere in the table
• Every row consists entirely of its column values and doesn't somehow contain any additional data

Posted Date: 1/18/2013 4:26:49 AM | Location : United States

Ask an Expert

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

Write discussion on Relational algebra - sql
Your posts are moderated

Write your message here..

Related Questions

Multiple assignment - sql, Multiple Assignment- SQL SQL supports mult... 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

Parameter modes - pl sql, Parameter Modes: You do not require to speci... Parameter Modes: You do not require to specify a parameter mode for the input bind arguments (those used, for illustration, in the WHERE clause) as the mode defaults to IN. Th

Order of evaluation-pl/sql expressions , Order of Evaluation When you do... Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT

In operator-comparison operators, IN Operator The operator IN tests the ... IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do

Keyword and parameter description in pl sql, Keyword and Parameter Descript... Keyword and Parameter Description: label_name: This is an undeclared identifier which optionally labels the PL/SQL block. When used, label_name should be enclosed by the do

Second step at defining type sid in sql, Second Step at defining type SID i... Second Step at defining type SID in SQL CREATE TYPE SID AS VARCHAR(5) ; Explanation: TYPE SID announces that a type named SID is being defined to the system.

Cursor variables, What Are Cursor Variables  ? The Cursor variables ar... What Are Cursor Variables  ? The Cursor variables are like C or Pascal pointers that hold the memory location (address) of some item rather of the item itself. Therefore, decl

Parameter and keyword description - open-for statement, Parameter and Keywo... Parameter and Keyword Description: cursor_variable_name: This identifies a cursor variable or the parameter formerly declared within the present scope. host_cursor_va

Referencing records, Referencing Records Unlike the elements in a coll... Referencing Records Unlike the elements in a collection, that are accessed using subscripts, the fields in a record are accessed by name. To reference an individual field, you

Using bulk collect clause- bulk bind performance improvement, Using the BUL... Using the BULK COLLECT Clause The keywords BULK COLLECT specify the SQL engine to bulk-bind output collections before returning them to the PL/SQL engine. You can use these ke