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Projection and Existential Quantification - SQL
Intuitively it might seem that projection in SQL is simply a matter of specifying the required columns in the SELECT clause, as in Example.
Example: Projection (incorrect)
Student StudentId is enrolled on some course.
SELECT StudentId FROM IS_ENROLLED_ON
Unfortunately, though, if some student is currently enrolled on more than one course (as indeed student S1, Anne, is in our example database), then the row giving that student's id appears twice in the result, which because of that duplicate appearance does not represent a relation. To avoid multiple appearances of the same row SQL requires you to write the word DISTINCT. (The key word ALL can be given instead of DISTINCT, clarifying that duplicate rows are not to be eliminated. As ALL is the default option).
Using Cursor Attributes: Every cursor has 4 attributes: %NOTFOUND, %FOUND, %ISOPEN, and %ROWCOUNT. If appended to the cursor name, they return the helpful information about
Literals A literal is an explicit numeric, string, character, or Boolean value not represented by an identifier. Numeric literal 147 and the Boolean literal FALSE are some of
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Parameter and Keyword Description: collection_name: This keyword identifies the index-by table, nested table, or varray formerly declared within the present scope. cu
MECHANISTI S THEORY-HAECKEL (1866) - Haeckel stating that after each catalysm, some new organism suddenly forms as a chance event in one stride from inanimate matter and sub
Named Notation The second procedure call uses the named notation. An arrow (=>) serve as the relationship operator that associates the formal parameter to the left of the arro
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
a. Write an anonymous block that contains a PL/SQL function. Given an order number orderNo, the function will calculate the total number of the parts in the order. Then the anonym
set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_divide then d
Using PRIOR and NEXT The PRIOR(n) returns the index number that precede index n in a collection. The NEXT(n) returns the index number which succeed the index n. If n has no pr
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