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Special cases of projection
This section describes the identity projection, r {ALL BUT}, and the projection on no attributes, r { }, which yields TABLE_DUM when r is empty, otherwise TABLE_DEE. As we have already seen, the identity projection is represented in SQL by SELECT * FROM t, but SQL does not recognize the existence of column less tables and so SELECT FROM t is not supported.
Semidifference via NOT IN and a subquery SELECT StudentId FROM IS_CALLED WHERE Name = 'Devinder' AND StudentId NOT IN (SELECT StudentId FROM IS_ENROLLED_ON WHER
THEO R Y OF PANSPERMIA - Arrhenius (1908) postulated the cosmic panspermia theory that claims that organisms existed throughout the universe, and their spores, etc., could
Updating a Variable Assignment of an attribute value in a variable of a structured type Synatx: SET SN.C = 'S2'; As in Example the entire statement is equivalent to a
Parameter and Keyword Description: type_name: This identifies a user-defined type specifier that is used in the subsequent declarations of the objects. AUTHID Clause:
CHECK Constraints in SQL A CHECK constraint is a table constraint defined using the key word CHECK, as already illustrated in several examples in this chapter. In particular,
User-Defined Exceptions The PL/SQL defines the exceptions of your own. Dissimilar to the predefined exceptions, the user-defined exceptions should be declared and should be rai
%TYPE: This attribute gives the datatype of a formerly declared collection, cursor variable, object, field, record, database column, or variable. Datatype: This is simply
Scoping Within the similar scope, all the declared identifiers should be unique. So, even if their datatypes differ, the variables and parameters cannot share the similar name.
FOR-LOOP While the number of iterations through a WHILE loop is unknown till the loop completes, then the number of iterations through a FOR loop is known before the loop is ent
Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.
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