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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 different from that used to declare local variables. Example is SQL's counterpart of that example in the theory book but, as you know, CREATE TABLE is used for base tables.
Example: A Variable Declaration
DECLARE SN SID DEFAULT SID ('S1');
DECLARE in place of VAR and DEFAULT in place of INIT. The effect is exactly the same apart from the fact that, as already noted, SQL's type SID (here assumed to be a distinct type). The key word DEFAULT is perhaps a strange choice as that word normally suggests action to be taken by the system when no specific action is explicitly demanded by the user. Here it is used to state explicitly an immediate assignment to the variable being declared.
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
If two relations R and S are joined, then the non matching tuples of both R and S are ignored in __________________.
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Write a program to implement the inverted file shown in the slides (Simple Index file, LabelID file and Data file). Use the Avail_List to point at the deleted Label IDs so that th
Dynamic Ranges The PL/SQL lets you determine the loop range dynamically at run time, as the example below shows: SELECT COUNT(empno) INTO emp_count FROM emp; FOR i IN 1..emp_cou
Indeterminacy in SQL Some SQL expressions are actually not function invocations at all in the mathematical sense, being indeterminate-invocations operating on identical input
Advantages of Wrapping The PL/SQL Wrapper convert the PL/SQL source code into a transitional form of the object code. By hiding the application internals, the Wrapper secure
Accessing Attributes: You can refer to an attribute only by its name not by its position in the object type. To access or modify the value of an attribute, you can use the dot
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
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