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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:
Ending Transactions A good quality programming practice is to commit or roll back every transaction explicitly. Whether you rollback or issue the commit in your PL/SQL program
Example of UNWRAP Operator - SQL Example here shows how unwrapping can be done in longhand in SQL. Example: Unwrapping in SQL Letting CONTACT_INFO_WRAPPED denote the res
Closing a Cursor The CLOSE statements disable the cursor, and the result set becomes undefined. An illustration of the CLOSE statement as shown: CLOSE c1;
Parameter and Keyword Description: record_type_name: This identifies the user-defined type specifier that is used in the subsequent declarations of the records. NOT N
Parameter and Keyword Description: cursor_variable_name: This identifies a cursor variable or the parameter formerly declared within the present scope. host_cursor_va
Biconditional - SQL The biconditional p ↔ q can be expressed in Tutorial D by p = q and the same is true of SQL. The question then arises as to whether, in SQL, p = q is equiv
ROWID and UROWID Internally, every database table has a ROWID pseudo column that stores binary values known as rowids. Each rowid shows the storage address of a row. A physical
How Exceptions Propagate ? Whenever an exception is raised, and if the PL/SQL cannot find a handler for it in the present subprogram or block, the exception propagates. That is
Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )
Calling Constructors: The Calls to a constructor are allowed wherever the function calls are allowed. Similarly to the functions, a constructor is called as a section of an ex
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