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UNION and OR - SQL
SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, such that IS_CALLED NATURAL JOIN IS_ENROLLED_ON, for example, can be an element of that clause but cannot stand alone as a table expression. Instead, UNION always connects table expressions that can stand alone, these being:
Adding Table Constraints ALTER TABLE ENROLMENT ADD CONSTRAINT NameNotNull CHECK (Name IS NOT NULL) ; ALTER TABLE ENROLMENT ADD CONSTRAINT PK_StudentId_CourseId PRIM
CLOSE Statement The CLOSE statement allows the resources held by a cursor variable or open cursor to be reused. No more rows can be fetched from the cursor variable or closed
Using Operator VALUE: As you may expect, the operator VALUE returns the value of an object. The VALUE takes its argument a correlation variable. For illustration, to return a
Effects of NULL for Multiple Assignments - SQL If the row expression given as the source for a multiple assignment evaluates to NULL, then NULL is assigned to each target. If
Cursor Variables Similar to a cursor, cursor variable points to the current row in the result set of a multi-row query. But, dissimilar a cursor, a cursor variable can be opene
The Package Body The package specification is implemented by the package body. That is, the package body has the definition of every cursor and the subprogram declared in the p
Other monadic - SQL In 2VL there are just 4 (2 2 ) monadic operators, of which negation is really the only "useful" one. When a third truth value is introduced we have 27 (3 3
Implicit Rollbacks Before execute the INSERT, UPDATE, or DELETE statement, the Oracle marks an implicit savepoint . When the statement fails, the Oracle rolls back to the save
What Is a Collection The collection is an ordered group of elements, all of similar type (for e.g. the grades for a class of students). Each element has a unique subscript whic
The SQL ‘CREATE TABLE' scripts for all the tables you have implemented. Note that your tables must correspond exactly to the ERD you have provided in 1. above, or you will lose ma
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