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Using NOT NULLBesides assigning an initial value, the declarations can impose the NOT NULL constraint, as the example below shows:acct_id INTEGER(4) NOT NULL := 9999;You cannot assign nulls to the variable define as NOT NULL. If you attempt the PL/SQL raises predefined exception VALUE_ERROR. The NOT NULL constraint should be followed by the initialization clause. For e.g. the declaration below is illegal:acct_id INTEGER(5) NOT NULL; -- illegal; not initializedRemember that the subtypes NATURALN and POSITIVEN are predefined as NOT NULL. For illustration, the declarations below are equivalent:emp_count NATURAL NOT NULL := 0;emp_count NATURALN := 0;In the NATURALN and POSITIVEN declarations, the type specifier should be followed by an initialization clause. Or else, you get a compilation error. For e.g. the declaration below is illegal:line_items POSITIVEN; -- illegal; not initialized
Nested Tables versus Index-by Tables The Index-by tables and nested tables are just similar. For e.g. They have similar structure and their individual elements are accessed in
Table Represents an Extension - SQL It describes how each tuple in a relation represents a true instantiation of some predicate and each true instantiation is represented by s
At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean’s wants to create a trigger that automatically updates the stock level of all pr
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
Closing a Cursor Variable The CLOSE statement disables the cursor variable. After that, the related result set is undefined. The syntax for the same is as shown below: CLOS
Benefit of the dynamic SQL: This part shows you how to take full benefit of the dynamic SQL and how to keep away from some of the common pitfalls. Passing the Names of Sc
Using Operator REF: You can retrieve refs by using the operator REF that, like VALUE, takes as its argument a correlation variable. In the illustration below, you retrieve one
INSERT Command in SQL Loosely speaking, INSERT takes the rows of a given source table and adds them to the specified target table, retaining all the existing rows in the targ
%ROWCOUNT The %ROWCOUNT yields the number of rows affected by the INSERT, UPDATE, or DELETE statement, or returned by a SELECT INTO statement. The %ROWCOUNT yields zero when a
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