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Short-Circuit Evaluation When computing a logical expression, the PL/SQL uses short-circuit evaluation. That is, the PL/SQL stops computing the expression as soon as the result can be determined. This permits you to write the expressions that might otherwise cause an error. Now consider the following OR expression:DECLARE...on_hand INTEGER;on_order INTEGER;BEGIN..IF (on_hand = 0) OR ((on_order / on_hand) < 5) THEN...END IF;END;Whenever the value of on_hand is zero, the left operand yields TRUE, so the PL/SQL require not compute the right operand. If PL/SQL were to compute both operands before applying the OR operator, the right operand would cause a division by the zero error. In any case, it is a poor programming practice to rely on the short-circuit computation.
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
INSERT Statement The INSERT statement adds fresh rows of data to the specified database table or view. Syntax:
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
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
Using Operator DEREF: You cannot navigate through refs within the PL/SQL procedural statements. Rather than, you should use the operator DEREF in the SQL statement. The DEREF
Using the FORALL Statement The keyword FORALL instruct the PL/SQL engine to bulk-bind input collections before sending them all to the SQL engine. Though the FORALL statement
Some Varray Examples In SQL Plus, assume that you define an object type Project, as described below: SQL> CREATE TYPE Project AS OBJECT ( 2 project_no NUMBER(2), 3 title VARCHA
Main features of PL/SQL A good way to get familiar with PL/SQL is to look at a sample program. The below program processes an order for tennis rackets. At first, it declares a
Existential Quantification - SQL Existential quantification-stating that something is true of at least one object under consideration-can be expressed by OR(r,c), meaning tha
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
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