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Multiple Assignment- SQL
SQL supports multiple assignment to local variables and also applies multiple assignment semantics in SET clauses of UPDATE statements, but does not support multiple assignment in connection with updates on table targets. Thus, SQL has no counterpart to the theory book's Example, simultaneously deleting from both COURSE and IS_ENROLLED_ON. If we assume that there must be at least one enrolment for each course, and that students can enroll only on existing courses, deferred constraint checking has to be used, as shown in Example here.
Example: Withdrawing course C3 and deleting any enrolments on C3
Assume the definition of IS_ENROLLED_ON includes
CONSTRAINT Course_must_exist_for_enrolment
FOREIGN KEY (CourseId) REFERENCES COURSE ON DELETE NO ACTION
and the definition of COURSE includes
CONSTRAINT Enrolment_must_exist_for_course
CHECK ( CourseId IN (SELECT CourseId FROM IS_ENROLLED_ON)
Variable Declaration - SQL SQL's support for variables is very similar to Tutorial D's, except that the syntax for creating persistent variables-base tables-is quite differen
Product-specific Packages The Oracle and different Oracle tools are supplied with the product-specific packages which help you to build the PL/SQL-based applications. For illus
Package STANDARD package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available a
Example of ADD CONSTRAINT in SQL Example: Alternative formulation for MAX_ENROLMENTS ALTER TABLE IS_ENROLLED_ON ADD CONSTRAINT MAX_ENROLMENTS CHECK ((SELECT COUNT (*)
UPDATE Statement The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:
SQL outer join SELECT * FROM IS_CALLED NATURAL LEFT JOIN IS_ENROLLED_ON Note that adding LEFT to an invocation of CROSS JOIN has no effect unless the right-hand operand
LOOP Statements The LOOP statements execute a series of statements at multiple times. The loops enclose the series of statements that is to be repeated. The PL/SQL provides typ
Create a view named CustomerAddresses that shows the shipping and billing addresses for each customer in the MyGuitarShop database. This view should return these columns from the
Multiple Assignment- SQL SQL supports multiple assignment to local variables and also applies multiple assignment semantics in SET clauses of UPDATE statements, but does not
Cursor Variables As Parameters You can declare the cursor variables as the formal parameters of the functions and procedures. In the illustration below, you define the REF CUR
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