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Type versus Representation Confusion in SQL
This describes how a value might have two or more distinct representations. For example, user-defined type POINT might have a declared possrep based on Cartesian coordinates and another based on polar coordinates. SQL has a system-defined type, TIMESTAMP, for values representing points in time, a timestamp being represented by a date, a time of day, and-optionally-a time zone, expressed as a displacement from UTC. Clearly any timestamp can be expressed in several different ways, using different time zones.
Three o'clock in the afternoon of December 31st, 2011 in UK, for example, is the same time as two o'clock in the morning of January 1st, 2012 in New Zealand. SQL treats those two representations as distinct values that compare equal, in like fashion to its treatment of character strings with trailing blanks, with similar consequences. If instead it had treated them as distinct representations of the same value, then the issue of indeterminacy would not have arisen.
Bulk Fetching The illustration below shows that you can bulk-fetch from a cursor into one or more collections: DECLARE TYPE NameTab IS TABLE OF emp.ename%TYPE; TYPE S
%ISOPEN The %ISOPEN yields TRUE if its cursor or cursor variable is open; or else, the %ISOPEN yields FALSE. In the illustration, you use the %ISOPEN to select an action:
Advantages of Subprograms The Subprograms give extensibility; that is, tailor the PL/SQL language to suit your requirements. For illustration, if you require a procedure which
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Projection in SQL - correct version Student StudentId is enrolled on some course. SELECT DISTINCT StudentId FROM IS_ENROLLED_ON In more complicated examples it is someti
Information Hiding With the information hiding, you see only the details that are significant at a given level of algorithm and data structure design. The Information hiding
what is the use of declare keyword
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 )
Deriving Predicates from Predicates in SQL The corresponding section in the theory book describes how predicates can be derived from predicates using (a) the logical connectiv
Packaging Cursors You can split a cursor specification from its body for placement in a package. In that way, you can change the cursor body without changing the cursor spec
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